A Tour of the Cell

Important words and concepts from Chapter 7, Campbell & Reece, 2002 (1/14/2005):

by Stephen T. Abedon (abedon.1@osu.edu) for Biology 113 at the Ohio State University

Course-external links are in brackets

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(1) Chapter title: A Tour of the Cell

(a) “…any one cell embodying as it does the record of a billion years of evolution, represents more an historical than a physical event…. You cannot expect to explain so wise an old bird in a few simple words.” Max Delbrück (as quoted by Stent, in Max Delbrück, 1906-1981, 1982, Genetics 101:1-16)

(b) “In an ideal world, biological processes would be understood at the molecular level by first identifying all the participating components and then by deducing their roles in the system through experiment. In reality, knowledge of each component is hard-won, and the temptation to assume that the key players are those that are currently known, ever-present.” (Adrian Bird, DNA methylation de novo, 1999, Science 286:2287-2288)

How to do Biology 113, Phase II

Now that we are just past the first exam and you are wondering what happened/how to improve…

1. The questions come from the notes that I hand out; study anything else (for the exam) and you are not being efficient. Reading the text is a great way to become familiar with and otherwise come to understand the concepts. That’s great, and should be the first thing you do as we move along in the course. However, I make no effort to pull exam questions directly from your text (except for assigned problems or for bonus questions on exams). Therefore you are not working efficiently if you are studying from your text, except to the degree that going back to your text aids in your understanding of the material. Similarly, while in the lectures I try to highlight the material, particularly that which is more difficult to understand, I do not write exam questions directly from what I present in the classroom (again, except for bonus questions on exams). Your text and lectures are a great way of repetitively increasing your familiarity and understanding of the material, but your lecture notes—the third in this triad of repetition—are where the exam questions come from.

2. Reading is not necessarily equivalent to studying. That doesn’t mean that you shouldn’t read, but studying involves trying to understand concepts and forcing information into your brain, and often those processes can be quite strenuous. If are not straining to some degree (other than fighting the studying process) then you likely are not so much studying as reviewing. The latter is a poor substitute for the former.

3. Putting in more time is not necessarily as important as studying well, efficiently, or effectively. Clearly if you studied for 20 hours for the first exam in this course and did not earn at least a B (and preferably a much higher grade) then you really need to reexamine how it is that you study to make much better use of your time.

4. You are not putting in a lot of time in until you are putting in excess of ~20 hours/week to studying biology/attending class and lab. But remember that seven hours of that 20 is spent in class or in lab and even just one hour spent per period per week works out to another five hours committed to biology.

5. If you don't learn/understand the material before going on to the next topic/material, when will you learn the old material? You won’t have enough time to learn material for the first time while you are studying for an exam. Furthermore, for most people learning thrives on repetition over relatively long spans of time. Such long-term repetition is not possible if you put off studying until exam time. Instead, you have to pause at difficult concepts when we first encounter them and at least make a cursory effort towards gaining some understanding.

6. Organizing the material is not equivalent to studying for exams (though certainly it helps you prepare for studying). If you are copying down material or even triaging while you are preparing for an exam, just keep in mind that while you may feel very productive while you are doing this, you aren’t actually studying (or at least not studying very intensively) for that exam. Organizing is great, can be very time consuming, but, like reading, it isn’t really studying.

7. If you want to do well, you must learn the majority of the material really, really well. You need to go for both breadth and depth. I will be testing you on both. If you blow off learning material, or otherwise don’t have time to get to it, you are simply taking a chance that this material will not be found on the exam. Typically it is very easy for me to tell when the breadth or depth of a student’s grasp of the material is not great. Often I may be accused of being picayune or of not adequately testing a student on what they do know—but my goal is to get you to a point where you both really know biology and really know how to study biology, and I think my exams do a wonderful job of determining the degree to which you have addressed both goals.

8. Try triaging, i.e., concentrate on learning and memorizing that material that (a) you don't know/have memorized and (b) have some reasonable probability of learning. But don’t fall into the trap of triaging away a large chunk of material simply because you haven’t given yourself sufficient time to study for an exam. Your triaging should be done days before the actual exam. And then, if you have time, you can go back to that material you discarded as being hopeless. But don’t, in the process, stress yourself out. That can sometimes be worse than just ignoring some material since stress can make you under perform even on material you do know well.

9. Part of studying for the exam should involved IDing that material to concentrate your studying on. Part of your college education is going to involve learning how to predict what an individual (your professor) cares about versus what serves simply as extraneous fluff. One of the secrets of college-level success is being able to focus on the material that is most important or most likely to end up as an exam question.

10. If you can't at least make a reasonable attempt at knowing the material to the point where you can recite it from memory, then you are not doing an adequate job of studying for an exam. One can similarly say that if you don’t reach a certain level of understanding of the material over the course of your studying then similarly you are not doing an adequate job studying, and it should be stressed that it is a whole lot easier to memorize material you understand (and, of course, that you care about) than it is to memorize material that you do not understand. Understanding allows derivation, and derivation (deductive along with inductive reasoning) is basically what much of biology is all about.

11. Don't put off learning the material until the night before the exam. And don’t forget to get a good night’s sleep prior to the exam. Take care of yourself. Treat yourself well and your self will respond by performing at a high level when that becomes necessary. An exam is like an athletic event. It takes training to do well, and it also takes peaking on the day of the event. Nobody I’ve ever met prepares to run a marathon by pulling an all nighter the night before nor spends that time running, running, and then running some more. The night before the event is a time to take care of yourself so that you will be in peak form when it comes time to prove yourself. Similarly, stressing yourself out by studying the day of the exam may allow you to learn material you really should have had down pat the night before (if not days prior), but at what cost in your ability to calmly and effectively understand and then correctly answer exam questions?

12. Studying is not easy, no way, no how (and that's why you get summers off). Indeed, studying towards a science degree can be so difficult that you might consider the pros and cons of prioritizing much more into your life except studying. But don’t forget that you need to have a life, too. If you aren’t enjoying yourself, then you may end up considering your classes to be a burden, but it is far easier to do something within the context of pleasure than to persevere in the face of pain. Do yourself a favor, do what it takes to live a long, kind, and enjoyable life.

BASIC PROPERTIES OF CELLS

(2) Cells

(a) Cells are the fundamental units distinguishing living from non-living entities

(b) Cells are membrane-enclosed, DNA-containing, metabolizing, and self-replicating

(3) Organelle

(a) Organelles are sub-cellular, multimolecular, organic machines

(b) Some organelles are surrounded by membranes (membrane-bound organelle)

(d) [organelle (Google Search)] [organelles (Caduceus MCAT Review)] [index]

(4) Prokaryote

(a) Prokaryotes are organisms whose cells lack nuclei

(b) Prokaryotic cells generally lack membrane-bound organelles

(d) Bacteria are an example of prokaryotic organisms (in addition to the previous link, see also the chapters 18 and 27 of your text)

(e) See Figure 7.4, A prokaryotic cell

(f) [prokaryote (Google Search)] [index]

(5) Eukaryote

(a) Eukaryotes have cells that contain nuclei

(b) Generally, eukaryotic cells contain membrane-bound organelles in addition to the membrane-bound nuclei

(c) Individual eukaryotic cells also tend to be quite a bit larger than individual prokaryotic cells (e.g, prokaryotic cells are about the size of the mitochondria or chloroplasts in Figures 7.7 and 7.8)

(d) Eukaryotes are typically unicellular (i.e., protozoa ) but there are many (and you are more familiar with) multicellular eukaryotes (i.e., plants, fungi, animals)

(e) See Figures 7.7 and 7.8 (for comparison to Figure 7.4): Overview of an animal cell, Overview of a plant cell, and A prokaryotic cells (respectively)

(f) Note in Figures 7.7 and 7.8 the various organelles, both membrane-bound and not membrane bound

(g) [eukaryote (Google Search)] [virtual plant cell (Matej Lexa)] [index]

(6) Plasma membrane

(a) The plasma membrane is the membrane surrounding and defining the limits of individual cells

(b) Not all membranes associated with a cell are the plasma membrane

(d) Note that the rate of nutrient acquisition and waste removal by a cell is proportional to area of plasma membrane (see "cells are small" below)

(e) See Figure 7.7, Overview of an animal cell

(f) [plasma membrane (Google Search)] [the cell membrane (Online Biology Book)] [plasma membrane (Caduceus MCAT Review)] [index]

(g) For more on membranes and membrane function, see the chapter 8

(7) Cytoplasm

(a) The cytoplasm is the stuff contained by the plasma membrane

(b) The cytoplasm consists of water solution, macromolecules, salts, various non-membrane-bound organelles, and a number of structural components

(d) See Figure 7.7, Overview of an animal cell

(e) [cytoplasm (Google Search)] [cytoplasmic constituents (Timothy Paustian’s Microbiology Textbook)] [index]

(8) Cytosol

(a) The cytosol is the water solution that makes up the cytoplasm (that is, the cytoplasm is the swimming pool while the cytosol is the water, you are an organelle… ha, ha)

(b) See Figure 7.7, Overview of an animal cell

(d) [cytosol (Google Search)] [index]

(9) Cells are small

(a) The size of cells is limited by the plasma-membrane-area-to-cytoplasmic-volume ratio

(b) The more cytoplasm a cell has, the more plasma membrane it needs to carry off wastes and obtain nutrients through

(c) As cell volumes increase in size, the ratio of surface area to interior volume decreases (these arguments are based simply on geometry, i.e., the formula for the volume of a solid versus the formula for the surface-area of a solid; the former increases as a cube function while the latter increases only as a square function)

(d) Consequently, bigger and bigger cells have greater and greater problems feeding themselves, ultimately limiting the useful size that cells may obtain

(e) One way around this surface-area constraint on cell size is the formation of various structures that serve either to increase the area of the plasma membrane without significantly increasing cytoplasmic volume (e.g., infolding of the plasma membrane) or to develop specialized cellular components that serve to increase membrane area without actually increasing the surface area of a cell’s plasma membrane (e.g., the endomembrane system of eukaryotic cells)

(f) See Figure 7.5, Geometric relationships explain why most cells microscopic?

(10) Compartmentalization

(a) In procaryotes the plasma membrane is additionally employed as an anchor for enzymes

(b) Since procaryotes typically lack internal membranes (i.e., no membrane-bound organelles) they have only limited membrane in which to anchor these enzymes

(d) Together these limitations circumscribe (i.e., restrict) the structural/morphological/even biochemical complexity individual procaryotes can attain

(e) By contrast, eucaryotic cells have numerous membranes in addition to the plasma membrane

(f) See Figure 7.7, Overview of an animal cell

(g) FAQ: What exactly is compartmentalization? The idea is that two otherwise incompatible chemical reactions can go on within the same cell so long as they don't (can't) come into contact with each other. How to keep them apart? By placing a membrane between the two reactions. Thus, within eukaryotic cells there exist numerous membrane-enclosed compartments such as lysosomes (and the rest of the endomembrane system), mitochondria, etc. This allows eucaryotes to perform more sophisticated intracellular chemistry than can procaryotes.

(h) [cell compartmentalization (Google Search)] [index]

(11) Membrane-bound organelle

(a) An important distinction between prokaryotic and eukaryotic cells is for the most part the absence in the former and the ubiquitous presence in the latter of membrane-bound organelles

(b) A membrane-bound organelle is an organelle that is bounded, i.e., surrounded, by a lipid bilayer

(c) A major component of the membrane-bound organelles found in eukaryotic cells are members of what is known as the endomembrane system plus the various endosymbionts (e.g., mitochondria and chloroplasts)

(d) [membrane-bound organelle (Google Search)] [index]

ENDOMEMBRANE

(12) Endomembrane system

(a) Many of the eukaryotic membranes form an interconnected or otherwise related network called the endomembrane system

(b) Via the endomembrane system, the membranes associated with different organelle members have different jobs

(c) Members of the endomembrane system may be either physically continuous with other members or not continuous but still communicating with other members of the endomembrane system via the release and fusion of transport vesicles

(d) See Figure 7.7, Overview of an animal cell

(e) Included in the endomembrane system are:

(i) the nuclear membrane

(ii) the endoplasmic reticulum (both rough and smooth)

(iii) the golgi apparatus

(iv) lysosomes

(v) vacuoles

(vi) the plasma membrane

(vii) transport vesicles

(f) [endomembrane system (Google Search)] [index]

(13) Nucleus

(a) In eukaryotic cells the cell DNA is separated from the cytoplasm

(b) Most of this DNA is contained within the cell’s nucleus

(d) During cell division, nuclear DNA is organized into chromosomes

(e) The structure that serves to divide the interior of the nucleus from the cytoplasm is the nuclear membrane

(f) Prokaryotic cells, by definition, lack nuclei (which is the plural of nucleus)

(g) See Figure 7.9, The nucleus and its envelope

(h) [cell nucleus (Google Search)] [the cell nucleus (Cell Biology Graduate Program—Univesity of Texas)] [cell nucleus (broken link) (Caduceus MCAT Review)] [the nucleus (Online Biology Book)] [index]

(14) Nuclear membrane

(a) The nuclear membrane is a double membrane

(b) The nuclear membrane’s inner membrane lines the interior volume of the nucleus

(d) Between the two nuclear membranes is a water solution-filled space that is continuous with a cell’s endomembrane system

(e) Connecting the interior volume of a nucleus with the external cytoplasm are numerous pores that form a fluid-filled bridge that crosses the nuclear membrane

(f) See Figure 7.9, The nucleus and its envelope

(g) [nuclear membrane (Google Search)] [nuclear membrane (broken link) (Caduceus MCAT Review)] [index]

(15) Ribosomes (free ribosomes, bound ribosomes)

(a) Ribosomes are non-membrane-bound organelles that are responsible for catalyzing protein synthesis

(b) Ribosomes come in two types differing only in their cellular location

(d) Bound ribosomes are bound to the cytoplasm side of certain members of the endomembrane system (rough ER and outer membrane of the nucleus)

(e) See Figure 7.10, Ribosomes

(f) [ribosome, free ribosome, bound ribosome (Google Search)] [ribosomes (Online Biology Book)] [ribosomes (lot’s of stuff but some loading problems; unsure of who author is)] [index]

(16) Nucleolus

(a) Among the many duties of the nucleus is the assembly of ribosomes

(b) Ribosomes are assembled in a region called the nucleolus

(d) See Figure 7.10, Ribosomes

(e) [nucleolus (Google Search)] [index]

(17) Endoplasmic reticulum (ER, cysternae, lumen)

(a) The endoplasmic reticulum is the endomembrane-system member that is continuous with (physically connected to) the outer nuclear membrane

(b) The endoplasmic reticulum is a network of membranous tubules and sacs called cysternae

(c) See Figure 7.11, Endoplasmic reticulum

(d) The space within the ER (lumen) is continuous with the space between the two membranes of the nucleus

(e) ER may be divided functionally and morphologically into two types: rough endoplasmic reticulum and smooth endoplasmic reticulum

(f) [endoplasmic reticulum, cysternae, lumen (Google Search)] [endoplasmic reticulum (Online Biology Book)] [index]

(18) Rough endoplasmic reticulum (rough ER)

(a) Rough endoplasmic reticulum derives its name from its rough appearance in electron micrograhs

(b) The rough ER is rough because it is bound with ribosomes (as is the outer membrane of nucleus), specifically with bound ribosomes

(i) extra-cytoplasmic-protein synthesis (i.e., proteins that are to be located within endomembrane system or secreted from the cell)

(ii) synthesis of integral-membrane-protein synthesis

(iii) some protein modification

(iv) membrane assembly

(d) [rough endoplasmic reticulum (Google Search)] [index]

(19) Smooth endoplasmic reticulum (ER)

(a) The portion of the endoplasmic reticulum that lacks bound ribosomes is known as the smooth endoplasmic reticulum

(b) See Figure 7.11, Endoplasmic reticulum (ER)

(i) lipid synthesis (particularly steroids)

(ii) carbohydrate metabolism (e.g., glycogen metabolism)

(iii) poison and drug detoxification

(d) [smooth endoplasmic reticulum (Google Search)] [index]

(20) Transport vesicles

(a) The nuclear membranes and ER are physically connected to each other

(b) The rest of the endomembrane-system members communicate via transport vesicles

(c) See Figure 7.16, Review: relationships among endomembranes, respectively

(d) See Figure 7.7, Overview of an animal cell

(e) Transport vesicles are membrane-enclosed, more-or-less spherical objects whose interior (lumen) is equivalent to the interior (lumen) of the ER

(f) Transport vesicles arise from various endomembrane-system members

(g) Transport vesicles transport their contents and membranes to endomembrane-system members by fusing their membranes with target members

(h) Targets can be many or all of the various endomembrane-system members

(i) [transport vesicle (Google Search)] [index]

(21) Golgi apparatus

(a) Central to the transport of vesicles is the golgi apparatus

(b) The golgi is the central intermediary connecting the plasma membrane , lysosomes , ER, and vacuoles via the release and reception of transport vesicles

(d) The golgi is also a site of manufacturing of certain materials

(e) FAQ: Golgi apparatus- a little more info dealing with the transport vesicles? The golgi isn't directly connected to either the ER or any of its various targets (e.g., the plasma membrane). Movement of membrane-enclosed "compartments" (i.e., vesicles) to and from the golgi allows the movement of membrane as well as endomembrane lumenal contents (e.g., proteins) to and from the golgi. These vesicles form by pinching off from existing endomembrane system components and deliver by fusing with endomembrane components. They allow a communication between endomembrane components without (drastically) disrupting compartmentalization. Vesicles differ according to their contents and targets. One job of the golgi is to properly match targets with contents.

(f) [golgi (Google Search)] [golgi apparatus and dictyosomes (Online Biology Book)] [index]

(22) Cis and trans faces of the golgi

(a) See Figure 7.12, The Golgi Apparatus

(b) The membranes of the golgi , in addition to having a cytoplasm -facing side and a lumen-facing side, additionally differ depending on their orientation to the ER

(d) The side of the golgi farthest from the ER is called the trans face

(e) The cis face receives transport vesicles from the ER and returns membrane (as transport vesicles) to the ER

(f) The trans face ships transport vesicles to the plasma membrane, vacuoles, or creates lysosomes

(g) Additionally, the trans face receives transport vesicles from the plasma membrane, vacuoles , etc.

(h) It is the golgi apparatus’s job to make sure that substances, including membrane components, are shipped to the correct locations

(i) The golgi determines where a substance should be shipped based on structural features of the substance (e.g., specific sequences of amino acids of polypeptides)

(j) [cis face golgi, trans face golgi (Google Search)] [index]

(23) Lumen protein, secreted protein, and membrane-protein synthesis

(a) Proteins destined for endomembrane system's lumen or for secretion from the cell are synthesized by bound ribosomes

(b) During synthesis polypeptide chains are extruded through the endomembrane into the lumen of the rough ER

(d) Many newly folded proteins also have carbohydrates (oligosaccharides) attached at this point making those proteins into glycoproteins

(e) Some proteins are only partially extruded through the membrane; these remain in the membrane and most of a cell’s integral membrane proteins (all?) are produced in this manner

(f) See Figure 7.16, Review: relationship among endomembranes

(g) Both rough ER lumen and membrane proteins are transported by transport vesicles to the cis face of the golgi apparatus

(h) Once in or otherwise associated with the golgi apparatus (e.g., as membrane components), substances may be further modified including the attachment of additional oligosaccharides

(i) The proteins—whether soluble within the lumen or as membrane proteins—may then be transported to other endomembrane-system members from the trans face of the golgi via transport vesicles

(j) Upon fusion with the plasma membrane (a process known as exocytosis), the lumen of the transport vesicle (a.k.a., secretory vesicle in this context) is continuous with the outside of the cell

(k) The proteins within secretory vesicles represent proteins to-be secreted by a cell

(l) [lumen protein, secreted protein, membrane-protein synthesis (Google Search)] [membrane synthesis and protein targeting mechanisms (Shy Arkin)] [index]

(24) Lysosomes

(a) Another target of golgi-modified proteins are lysosomes

(b) Lysosomes are created by the golgi apparatus

(d) The job of lysosomes is to provide a region that is separate from the cytoplasm in which cellular components may be digested back to their component parts

(e) This separation (compartmentalization) protects the cell from uncontrolled auto-digestion

(f) [lysosome (Google Search)] [lysosomes (Caduceus MCAT Review)] [lysosomes (Online Biology Book)] [index]

(25) Vacuoles

(a) Various other components of the endomembrane system are termed vacuoles

(b) These generally are specialized, membrane-enclosed structures that are connected with the golgi apparatus via transport vesicles

(d) See Figure 7.15, The plant cell vacuole

(e) See Figure 7.8, Overview of a plant cell

(f) Other examples are contractile vacuoles (see Figure 8.12, Evolutionary adaptations for osmoregulation in Paramecium) and food vacuoles (protozoa)

(g) FAQ: What is a vacuole, other than a component of the endomembrane system that are connected to the golgi? Vacuoles aren't physically connected to the golgi. A vacuole is just a big vesicle. That is, vacuoles are yet another part of the endomembrane system that is not physically continuous with the ER, the golgi, the plasma membrane, etc. There are a number of different, specialized endomembrane components that are called vacuoles including food vacuoles (where stuff engulfed during endocytosis ends up), contractile vacuoles (which pump water out of the highly hypertonic cytoplasm of protozoa), and, of course, the central vacuole in plant cells which is a storage area that serves, in part, to take up space within the plant cell. Cytoplasmic components are expensive (mitochondria, chloroplasts, ribosomes, proteins, etc.). Central vacuoles allow plant cells to have a relatively large volume while simultaneously having a relatively small cytoplasmic volume. Other functions are listed in your text.

(h) [vacuole (Google Search)] [vacuoles and vesicles (Online Biology Book)] [index]

(26) Phagocytosis and food vacuoles

(a) Transport-like vesicles called food vacuoles may be created by the formation of vesicles at the plasma membrane (a process known as phagocytosis or endocytosis)

(b) Enclosed within these food vacuoles may be trapped extra-cellular material

(c) These food vacuoles are then fused with lysosomes which allows the digestion of the now-lumenal, formerly extra-cellular material

(d) See Figure 7.14, The formation and functions of lysozome

(e) [phagocytosis, food vacuole (Google Search)] [index]

MITOCHONDRIA

(27) Gram-negative bacteria

(a) Gram-negative bacteria are a type of bacteria that includes many pathogenic bacterial types, such as Escherichia coli (though, in fact, many more are not pathogenic than are pathogenic)

(b) The typical cellular anatomy of a Gram-negative bacterium includes, outside going in:

(i) outer membrane

(ii) cell wall

(iii) periplasmic space

(iv) inner membrane

(v) cytoplasm

(vi) DNA

(vii) ribosomes

(c) (Gram-positive bacteria, another type of bacteria, are similar in their cellular anatomy to Gram-negative bacteria but lack the outer membrane and also lack the periplasmic space)

(d) Gram-negative bacteria, like most bacteria, divide by binary fission

(e) Many Gram-negative bacteria, as well as Gram-positive bacteria generate their ATP via cellular respiration, by mechanisms very similar to how the mitochondria of eukaryotic cells generate ATP, also via cellular respiration

(f) [Gram-negative bacteria (Google Search)] [index]

(28) Mitochondria

(a) Mitochondria are organelles found in the cytoplasm of most eukaryotes

(b) This organelle is responsible for cellular respiration, the mechanisms by which most eukaryotes generate the majority of their ATP

(c) See Figure 7.17, The mitochondrion, site of cellular respiration

(d) Mitochondrial structures, analogous to those found in Gram-negative bacteria, include going from the outside in:

(i) outer membrane

(ii) intermembrane space (periplasmic-space equivalent)

(iii) inner membrane

(iv) mitochondrial matrix (cytoplasm equivalent)

(v) DNA

(vi) ribosomes

(e) Mitochondria divide by binary fission

(f) Notably absent from the above list is the Gram-negative cell wall but, nevertheless, mitochondria are essentially gram-negative bacterium in terms of structure as well as their genetics and biochemistry

(g) Though membranous, note that mitochondria are not a part of endomembrane system

(h) We will consider the origin of mitochondria in greater detail in chapter 28 of your text; suffice for now with our simply noting that mitochondria in fact are Gram-negative bacteria that live within the cytoplasm of most eukaryotic cells and which are responsible for carrying out the cellular respiration from which euckaryotic cells derive most of their ATP

(i) See Figure 7.7, Overview of a animal cell

(j) [mitochondria (Google Search)] [mitochondria (Online Biology Book)] [origin and evolution of the related organelles: mitochondrion, chloroplast, and peroxisome (The Society for the Study of the Origin and Evolution of Life)] [index]

(29) Cristae

(a) The inner membrane of mitochondria is folded to increase membrane area

(b) The existence of these folds, called cristae, serves to increase the amount cellular-respiration enzymes found only in the mitochondria inner membrane, and therefore to increase the cellular-respiration capacity of a given mitochondrian

(c) See Figure 7.17, The mitochondrian, site of cellular respiration

(d) [cristae (Google Search)] [index]

CHLOROPLASTS

(30) Cyanobacteria

(a) Cyanobacteria are Gram-negative-like bacteria that live particularly in water (they are a constituent of pond scum)

(b) Cyanobacteria are unique among gram-negative bacteria in terms of their ability to photosynthesize using a mechanism that is very similar to that employed by green plants

(31) Chloroplast (stroma)

(a) Chloroplasts are organelles found in plants and algae that are responsible for photosynthesis (the conversion of energy and CO₂ into sugar)

(b) See Figure 7.18, The chloroplast, site of photosynthesis

(i) outer membrane

(ii) intermembrane space

(iii) inner membrane

(iv) stroma (the cytoplasm equivalent, liquid found external to the thylakoids)

(v) DNA

(vi) ribosomes

(d) Chloroplasts, like Gram-negative bacteria, mitochondria, and cyanobacteria, divide by binary fission

(e) Chloroplasts are not a part of endomembrane system

(f) Yes, chloroplasts, like mitochondria, are essentially gram-negative bacteria, though chloroplasts particularly are not-free-living cyanobacteria

(g) Other, non-photosynthesizing bacteria-like plastids also exist in plants

(h) See Figure 7.8, Overview of a plant cell

(i) [chloroplast (Google Search)] [chloroplast links (MicroDude)] [index]

(32) Thylakoids (grana, thylakoid space)

(a) Thylakoids are membrane-bound organelles found within chloroplasts

(b) These organelles look like flattened disks (they have a large surface they expose to sun)

(d) The thylakoids are derived from the inner membrane of chloroplasts

(e) The thylakoids are the actual site of photosynthesis within chloroplasts (particularly the light reaction)

(f) The interior of thylakoids is called the thylakoid space

(g) See Figure 7.18, The chloroplast, site of photosynthesis

(h) [thylakoid, grana, thylakoid space (Google Search)] [index]

CYTOSKELETON

(33) Cytoskeleton

(a) The cytoplasm of eukaryotic cells contains a network of protein fibers

(b) There are three classes of fibers:

(i) microtubules

(ii) microfilaments

(iii) intermediate filaments

(c) See Table 7.2, The structure and function of the cytoskeleton

(d) The cytoskeleton members perform various functions as discussed below

(e) [cytoskeleton (Google Search)] [cytoskeleton (Caduceus MCAT Review)] [cytoskeleton (Online Biology Book)] [index]

(34) Microtubules (tubulin)

(a) Microtubules are the largest-diameter cytoskeleton components

(b) Microtubules can be very long (e.g., on the order of cell dimensions)

(d) Microtubules serve to shape and support the cell

(e) Microtubules are easily dismantled by removing tubulin subunits; they are also easily lengthened by adding tubulin subunits

(f) Microtubules serve as tracks along which organelles can move

(g) See Figure 7.21, Motor molecules and the cytoskeleton

(h) An example of this movement of organelles is the movement of transport vesicles about the cell between endomembrane-system components

(i) [microtubules, tubulin (Google Search)] [index]

(35) Centrosome (centriole)

(a) The centrosome is essentially the central microtubule-supporting member

(b) Microtubules radiate out from a single centrosome, rigidly supporting cell structure

(d) See Figure 7.22, Centrosome containing a pair of centrioles

(e) The centrioles are replicated during cell division so that each daughter cell receives one centrosome

(f) [centrosome, centriole (Google Search)] [index]

(36) Cilia and flagella

(a) Microtubules also make up cilia and flagella

(b) These are organelles that project from the cytoplasm, encased within the plasma membrane, out into the extracellular environment

(d) Cilia are shorter, oar-like structures that are typically many in number per cell

(e) Both cilia and flagella are involved in cell motility (including many protozoa; sperm, for example, have flagella)

(f) See Figure 7.23, A comparison of the beating of flagella and cilia

(g) Cilia are also involved in movement of material over surfaces of cell (e.g., ciliated cells line the respiratory system and push foreign material out of the lungs, but are paralyzed by cigarette smoke, hence the smoker’s hack)

(h) See Figure 7.24, Ultrastructure of a eukaryotic flagellum or cilium

(i) The microtubules internally support the shape of cilia and flagella

(j) The microtubules also interact, partially sliding past one-another to allow cilia and flagella to bend (mechanism analogous to what makes muscles contract; also ATP-powered)

(k) See Figure 7.25, How dynein “walking” moves cilia and flagella

(l) [cilia, flagella, dynein (Google Search)] [cell movement (Online Biology Book)] [cilia and microvili slide show (follow slides backwards—to the left) (Microanatomy Web Atlas)] [index]

(37) Microfilaments (actin) (myosin)

(a) Mirofilaments consist of two twisted-together chains of actin-protein subunits

(b) Microfilaments are the smallest in diameter of the cytoskeleton components

(d) See Figure 7.27a, Microfilaments and motility

(e) ATP powers movement of actin filaments relative to myosin filaments

(f) The same arrangement of actin and myosin is involved in the dividing of cytoplasm (pinching together of plasma membrane) during cell division

(g) Microfilaments are also involved in projection of pseudopodia (amoeboid movement)

(h) See Figure 7.27b, Microfilaments and motility

(i) Microfilaments are also involved in cytoplasmic streaming (seen in plants)

(j) See Figure 7.27c, Microfilaments and motility

(k) Microfilaments also support microvilli (non-movable finger-like projections superficially resembling cilia)

(l) See Figure 7.26, A structural role of microfilaments

(m) [microfilament, actin (Google Search)] [index]

(38) Intermediate filaments

(a) Intermediate filaments are a more-structurally diverse array of cytoskeleton components

(b) Intermediate filaments have a diameter that is intermediate between that of microtubules (bigger) and microfilaments (smaller)

(d) Intermediate filaments serve to reinforce the shape of a cell as well as anchor various organelles

(e) [intermediate filament (Google Search)] [index]

(39) Extracellular matrix (collagen, proteoglycan)

(a) The extracelular matrix is the stuff that is found between and surrounding animal cells

(b) The extracellular matrix glues animal cells together

(c) The extracellular matix consists predominantly of protein collagen and high carbohydrate-content glycoproteins called proteoglycans

(d) These are the fibers and the gluey matrix in which these fibers are embedded, respectively

(e) See Figure 7.29, Extracellular matrix of an animal cell

(f) [extracellular matrix, collagen, proteoglycan (Google Search)] [index]

CONNECTIONS BETWEEN CELLS

(40) Attachments to plasma membrane (desmosomes, gap junctions, tight junctions)

(a) Various molecules and structures attach to the outside (as well as inside) of the plasma membrane

(b) On the inside is the cytoskeleton

(c) On the outside is the extracellular matrix

(d) Desmosomes: Plasma membranes can attach to adjacent cells for increased structural support of tissue [desmosome slide show (Microanatomy Web Atlas)]

(e) Gap Junctions: Protein tubes between adjacent cells form, for relatively small molecules (up to about 1000 dalton) a continuous cytoplasm between cells

(f) Tight junctions: Plasma membranes form junctions between them that are water tight

(g) See Figure 7.30, Intercellular junctions in animal tissues

(h) [membrane attachment, desmosomes, gap junctions, tight junctions (Google Search)] [index]