The cell

Question 1

Describe the importance of the nucleus.

E.g., where is it, what does it do, what does it look like?

Answer 1

• The nucleus is where nuclear (normal) DNA is found. The DNA doesn’t leave the nucleus!
• It is linear in structure, has open ends
• Diploid (has maternal and paternal genes)
• Is surrounded by a double bilayer membrane
• Contains nuclear pores

Question 2

What is the nucleolus?

nucLEOlus

Answer 2

A site of rRNA transcription and ribosome assembly.

Question 3

What is the rough ER?

Answer 3

Rough in structure = bumpy because it has ribosomes covering the ER.

The ribosomes translocate proteins into the ER lumen as those proteins are translated.

Question 4

What is made in the rough ER?

Answer 4

All proteins…

1. Bound for the ER itself
2. Golgi
3. Lysosomes
4. Endosomes
5. Plasma membrane
6. For secretion out of the cell
7. Some bound for other organelles

Question 5

Where are proteins that are bound for the cytosol made?

Answer 5

They are made on free floating ribosomes in the cytosol.

Question 6

Where does post-translational modification start?

What does post-translational modification even mean? What are some examples?

Answer 6

Cytosol, and eventually continues in the Golgi.

Post translational modification means that the protein that was translated gets further modified after it has been completed. An example of this is the formation of disulfide bonds, glycosylation, etc.)

Question 7

What is the smooth ER?

What is the SER’s function?

Answer 7

Function: lipid synthesis/modification.

NOT LIPID METABOLISM.

Question 8

Where does lipid metabolism occur?

Answer 8

The MITOCHONDRIA.

Question 9

Golgi Apparatus

Answer 9

The cellular “post office” for proteins. This is where organization and packaging of proteins occurs.

Also occurring here is post-translational modification, which is just a fancy way of saying further modification to proteins after they are already existing.

Question 10

How does the golgi work? Where do proteins go after they leave?

Answer 10

Since it’s a post office, it sends out “packages” of proteins that are excreted from the cell via vesicles.

The proteins can be destined for the plasma membrane, ER, or other organelles.

Question 11

Mitochondria

Answer 11

The site of lipid MODIFICATION.
They have their own DNA and variations in nuclear code.
Originated from the endosymbiotic theory.

Question 12

What is the endosymbiotic theory?

Answer 12

Has to do with mitochondria’s origin.
Says that:
A small aerobic prokaryote was engulfed by a larger prokaryote. This is where mito’s evolved from.

Why the name “endosymbiotic”? Because the aerobic prok and larger prok formed a symbiotic relationship, meaning they both benefitted from it.

Question 13

What is it about mitochondria that supports the endosymbiotic theory?

Answer 13

Mito have their own DNA, do their own replication, divide and replicate like a bacterium, and have double bilayer membrane.

Question 14

How do the pH values of the matrix and the intermembrane space compare?

Answer 14

Intermembrane space’s pH is more acidic (lower pH)
-due to the hydrogen ion gradient across the inner mitochondrial membrane.

Matrix pH is ~7.8, which is about 1.4 pH unites higher than that of the intermembrane space

Question 15

Predict the consequences of the insertion of H+ channels within the intermembrane.

Answer 15

Since the intermembrane space is more acidic, there are more H+ ion present within this space. Therefore, according to basic [] gradient rule, if a channel is introduced then there will be flow of the H+ ions from high to low []. Therefore, there will be more H+ ions within the mitochondrial matrix, which makes the matrix decrease in pH.

Since the hydrogen ion gradient runs along the inner mitochondrial membrane, and this gradient being crucial for the electron transport chain to function to GENERATE ATP, the insertion of H+ channels into the inner mitochondrial membrane would result in a decrease in production of ATP, since the H+ gradient was disrupted.

Question 16

What is thermogenin?

Answer 16

It is a protein channel in the inner mito membrane that allows for passage of protons.

Found in most mammals, eps young mammals (BROWN FAT) and animals that hibernate.

If a similar proton channel were to be opened up in the outer mito memb, this could also negatively impact ATP production due to loss of the proton gradient as protons leak out into the cytosol.

Question 17

Centrioles/Centromere

Answer 17

Centrosome: area of proteins and nucleating factors where centrioles are located.

Function: organize microtubules, flagella, and cilia. Important in cell division (pull apart sister chromatids)

Question 18

Lysosomes

• what do they do and why are they important?
• Where do they come from?

Answer 18

Think about it like lysol; it destroys germs.
Except that it’s much more badass than that. It is acidic, digests cell parts, fuses with phagocytes, and helps with apoptosis.

They form by budding from the Golgi.

Question 19

Peroxisomes

Answer 19

Think about what peroxide does; it disinfects wounds and other gross stuff.

So peroxisomes self replicate, detoxify molecules, and participate in lipid metabolism.

Question 20

Tubulin and its 2 types

Answer 20

Globular protein that polymerized to form microtubules

2 types: alpha and beta, form a deterodimer that is then assembled into long chains called protofilaments

Question 21

What makes up a microtubule?

Answer 21

13 protofilaments surrounding a hollow core MAKE UP ONE MICROTUBULE

Question 22

9 + 2 arrangement

Answer 22

Found in eukaryotic cilia and flagella
The “9” and “2” refer to nine doublets (two microtubules each) surrounding a center doublet (2 microtubules) in
a wheel-like design.

That would be a total of 20 microtubules—each one of those twenty microtubules being the hollow tube of 13 protofilaments just described.

Question 23

Three primary contributors to the cytoskeleton of the cell

Answer 23

1. Microtubules
2. Microfilaments (actin polymers)
3. Intermediate filaments

Question 24

Cytoskeleton

Answer 24

Scaffolding like network of microfilaments, microtubules, and intermediate filaments
FXN: provide structure, create a “highway” for intracellular transport

Question 25

Spindle apparatus

Answer 25

Array of microtubules that grows outward from the centrioles during mitosis to bind with the centromere of the chromosomes at the metaphase plate.

Effects division of a pair of sister chromatids into two separate chromosomes

Question 26

Where are cilia exclusively found in humans? (3)

Answer 26

1. Respiratory tract (mucociliary elevator)
2. Nervous system (emendymal cells)
3. Reproductive system (uterine tubes)

Question 27

In what important structures are microtubules found?

Answer 27

Any structure where cilia are found, in the flagella of sperm, and as part of the cytoskeleton and spindle apparatus.

Question 28

What would a disease that prevented microtubule production cause?

STORY TIME:

We know that microtubules are important in flagella, cilia, the cytoskeleton, and the spindle apparatus function.

So, think about what Cristina from GA suffered from in season 2 (?) and why that may have happened.

What about “swimmers”? Would they be impacted?

How would the structure of cells be potentially impacted?

Answer 28

Any dysfunction of microtubules.

Cells would generally have weakened cytoskeletons, and the cytoskeletal “highway” path for organelle, etc. transport would be disrupted.

Ciliated epithelial cells would lose fxn.

Cells would be unable to undergo mitosis or meiosis because the spindle apparatus is affected.

Infertility may result due to immobile sperm.

Extra-uterine pregnancy may occur since the ciliated cells that line the fallopian tubes and normally sweep the egg toward the uterus would be dysfunctional.

Question 29

What’s the difference between flagella and cilia?

What human cells have flagella?

Think about what you know about the mucociliary elevator and the top of intestinal epithelial cells.

Answer 29

Flagella are used for moving around cells. The only human cells that have flagella are sperm.

Cilia come off the lumen side of epithelial cells. They’re not used for movement of the cell. The purpose is for them to move other things towards or past the cell they are attached to.

e.g., epithelial intestinal lining cells: have microvilli that provide more surface area for more Na+/Glucose coupled transport channels, to ensure that glucose ends up being transported from the lumen of the GI tract into the extracellular fluid under the basal layer of these intestinal epithelial cells.

Question 30

What’s the difference between eukaryotic and prokaryotic flagella?

Answer 30

Ernie eukaryote likes to WHIP his dick out and hide it in a TUBE
—Translation: eukaryotic flagella move in a WHIPping motion and their microtubules are made of TUBulin

Pansy prokaryote SPINS when she walks since she is a FLAG twirler.
—Translation: prokaryotic flagella move in a simple SPINning motion and have SIMPLE helices that are made up of FLAGellin

Question 31

Phospholipids

• what are their properties?
• composition
• why are they important (what do they form?)
• what structure do they make?

Answer 31

Fats that make up the bilipid membrane layer. They have polar heads and 2 nonpolar tails.

General structure:
headgroup —phosphate—glycerol—–2 FA tails
1 FA tail has a cis double bond kink in it

When put in water, they spontaneously orient themselves in a sheet, that results in hydrophilic heads interacting with H2O and nonpolar tails mostly not interacting with H2O.

However, the tails at the end of this sheet partially interact with water, so the sheet’s structure gets modified even more by folding on itself so that a liposome (phospholipid “cell”) is formed. This way, no tails are in contact with water and the heads are happily interacting with the water.

Question 32

What is special about spingomyelin?

Answer 32

It has a high concentration of lipid rafts and lacks a glycerol.

Question 33

MCAT example question based off phospholipids:

What do the functional groups look like before and after a FA reacts with it to become a part of the phospholipid?

Answer 33

Since the FA is a long carboxylic acid chain and in the phospholipid structure is attached to the glycerol, there must be interaction between the glycerol and the FA tails.

The interaction is as follows: an OH group from the glycerol attacts the carbonyl C of the FA, splitting off water and forming a new ester group that is a part of the major molecule.

See this drawing on p 200 of the Altius book.

Question 34

Integral membrane proteins

Answer 34

Can have 1+ segments as a part of the phospholipid layer.

—e.g., INTEGRATED completely in the membrane

types: transport proteins

Question 35

Surface proteins/peripheral membrane proteins

Answer 35

Don’t enter the hydrophobic core, are found exclusively on the polar surface of the molecule

—e.g., pimp stand on the OUTSIDE of buildings looking for their hoes

Question 36

Transport proteins

Answer 36

Integral proteins that span the entire width of the bilayer membrane (i.e., transmembrane proteins) creating tunnels for the passage of ions, proteins, etc. thru the hydrophobic core.

Question 37

Membrane receptor

Answer 37

Any protein that specifically binds a signaling molecule (e.g., ligand) that initiates a cellular response.

Nonpolar (e.g., steroid hormone receptors) membrane receptors can be found within the cell in the nucleus since steroids/nonpolar molecules can diffuse thru the nonpolar core.

Polar ligand membrane receptors are located on the surface of the membrane, they don’t pass thru the hydrophobic core.

Question 38

Cholesterol

Answer 38

Amphipathic molecule with a steroid region and small polar region.

Lots are found inserted within phospholipids to stiffen, yet also add fluidity, to the bilipid membrane.

At higher temps, the nonpolar region interacts with the nonpoar tails of phospholipids, holding them in place and making the membrane more rigit.

At lower temps, the interactions between NP tails could cause crystallization, and the presence of the rigid steroid portion of cholesterol disrupts VdWi’s between FA tails, maintaining a level of fluidity.

Question 39

Fluid Mosaic Model

Answer 39

Refers to the dual layer model of a phospholipid membrane that is commonly shown to students.

The fluid part of the terms refers to the fact that the phospholipids can undergo lateral diffusion and can sorta move around within the bilipid membrane.

Question 40

Exocytosis

give an example (think of what Egbert taught us about AP’s in BIO 344)

Answer 40

Vesicle on the inside of the plasma membrane fuses with the plasma membrane, and dumps its contents into the extracellular envt.

ex: Ca++ enters the axon terminal once it’s V-gated channels are depolarized by the propogating AP. Once Ca++ diffuses into the cell, this causes vesicles containing NT’s to fuse with the membrane of the axon terminal and therefore dump NT’s into the synaptic cleft. The NT’s then go to the postsynaptic cell dendrites where the NT will bind to a ligand gated Na+ channel to cause depolarization of the next nerve cell.

Question 41

Endocytosis

Answer 41

Process where a cell takes up small particles by invagination of the plasma membrane to form a vesicle called an endosome.

Question 42

Phagocytosis

Answer 42

Type of endocytosis

A cell engulfs very large particles or bacteria

Receptor mediated.

Question 43

Pinocytosis

Answer 43

NON SPECIFIC endocytosis of ECF and very small particles and occurs in all cells

Question 44

Membrane Transport types (4)

Answer 44

1. Passive diffusion
2. Facilitated diffusion
3. Active transport
4. Secondary active transport

Question 45

What is facilitated diffusion

Answer 45

No ATP is required. One ion uses the [ ] gradient of another ion to drive it’s transport

Question 46

Hypertonic solution

Answer 46

When a cell is surrounded by a solution that has a HIGH [ ] of solutes.

There are more [ ] of ions outside the cell, and a lower [ ] of ions inside the cell.

There is less water outside of the cell and more water inside the cell.

In light of this, to try to get the equilibrium back, the cell dumps out as much water as possible to try to DILUTE the hypertonic solution.

Since lots of water leaves the cell, it shrivels. It’s also going to decrease the use of Na/K ATPase pumps, because the cell doesn’t want to pump more ions out into the already very high [ ] ion solution.

Question 47

Hypotonic solution

Answer 47

When a cell swells when it’s put into pure H2O solution.

There are more solutes in the cell in comparison to outside the cell.

In order to even out the solute/water ratio, water diffuses into the cell and solutes go out of the cell to try to even it out.

Since so much water goes into the cell, it swells and can even lyse. This is baaaaad.

THIS IS WHY YOU DON’T GIVE A PATIENT AN IV OF PURE H2O.

Question 48

Isotonic solution

Answer 48

There is an equal [ ] of ions outside of the cell as inside of the cell and there is no new flow of water.

Question 49

Secondary active transport

Answer 49

No direct coupling of ATP is required

Question 50

Tight junction

Answer 50

Waterproof, doesn’t allow membrane proteins or channels to move.

e.g., lining of the bladder, 
the linings that form the blood-brain barrier, 
the distal convoluted tubule, 
and
collecting duct of the kidney, etc.

Question 51

Gap junction

Answer 51

Occur between adjacent cells in many different
tissues throughout the body.

A few classic examples that allow electrical or chemical coupling between cells include:

1) the junctions between cardiac muscle cells, or between smooth muscle cells, which allow for rapid passage of an electrical potential between cells,
2) direct neuron-neuron coupling found in certain parts of the brain and in the retina of the eye.

Question 52

Adherens junctions

Answer 52

Strong mechanical attachments

ex) Found in epithelium and between cardiac muscle cells.

Question 53

Desmosomes

Where are these most common

What is a good example of what can happen if desmosomes are interfered with?

Answer 53

The strongest of the cellular junctions, they weld cells together, protecting against stress, but are NOT watertight.

• –Particularly common in stratified
  epithelium.

—Ex) An autoimmune disease that produces antibodies against the desmosome protein (desmoglein) leads to separation of skin layers and large, painful blisters.