Bio: Cell biology/Eukaryotic Cells

Question 1

RER (What gets made here?)
SER

**KNOW YOUR ORGANELLES

Answer 1

RER location of synthesis/modification of secretory, membrane-bound, and organelle proteins, post-translational modification of proteins

SER detoxification and glycogen breakdown in liver; steroid synthesis in gonads

Question 2

Golgi apparatus

Vesicles from ER fuse with cis/trans stack, go to medial stack, and leave cis/trans stack

Answer 2

modification and sorting of protein, some synthesis

1) Modification of proteins made in the RER
2) Sorting and sending proteins to their correct destinations
3) The Golgi also synthesizes certain macromolecules, such as polysaccharides to be secreted

traffic to and from golgi mostly unidirectional

Vesicles from ER fuse with cis stack, go to medial stack, and leave trans stack

Question 3

Lysosomes, what enzyme is present in lysosome and what does it do?

Peroxisomes, what does it do, produce, and what enzyme does it have?

Answer 3

lysosomes contain acid hydrolases that digest various substances (only when in acidic environments, so would not work if broke and went into cytoplasm)
Membrane bound organelle that is responsible for the degradation of biological macromolecules by hydrolysis
Organelles such as mito that have been damaged or are no longer functional may be degraded in lysosomes in a process termed autophagy (self eating), lysosomes also degrade large particle matter engulfed by cell by phagocytosis (ex. macrophages), crinophagy = lysosomal digestion of unnecessary (excess) secretory proteins

Peroxisomes metabolize lipids and toxins, contain enzymes that produce H2O2 as a by-product (dangerous chemical) but contains enzyme catalase which breaks H2O2 down to protect from peroxides and free radicals

Question 4

The nucleolus function? What enzyme works in there?

Answer 4

The nucleolus is a region within the nucleus which function as a ribosome factory, it consists of loops of DNA, RNA polymerases, rRNA, and the protein components of the ribosome
The nucleolus is the start site of transcription of rRNA by RNA pol I
Protein components of ribosome are not produced in the nucleolus; they are transported into the nucleus from the cytoplasm (all translation takes place in cytoplasm for ribosome) and the protein components of ribosome are assembled in the nucleolus
After partial assembly, the ribosome is exported from the nucleus, remaining inactive until assembly is completed in the cytoplasm

Question 5

The membrane of ER is at points contiguous with the outer nuclear membrane (The ER lumen is equivalent (contiguous with) the extracellular space)
The nuclear envelope is punctuated with large nuclear pores, what can go through? What is a nuclear localization sequence and how does it work?

Answer 5

Molecules smaller than 60 Kd, including small proteins can go through
Large proteins can go though if they have a nuclear localization sequence -> Proteins with nuclear localization sequence are translated on cytoplasmic ribosomes and then imported into the nucleus by specific transport mechanisms

Question 6

Where is pyruvate dehydrogenase located?

Answer 6

Matrix

Question 7

What does mito have that the whole cell also has? What does that thing do?

Answer 7

Mito possess their own genome which is far smaller than the cellular genome and consists of a single circular DNA molecule. It encodes rRNA, tRNA, and several proteins, including some components of the ETC and parts of ATP synthase although most mito proteins are encoded by nuclear genes

Question 8

Maternal inheritance

Answer 8

Mito exhibit Maternal inheritance which means the mito is inherited only from the mother, since the cytoplasm of the egg becomes cytoplasm of the zygote, sperm only contributes genomic nuclear DNA
Maternal inheritance departs from the rules of Mendelian genetics

Question 9

What are two sites of protein synthesis? What happens to proteins after each?

Describe pathway from RER

Answer 9

In Eukaryotes protein synthesis can either take place on ribosomes free in the cytoplasm or on ribosomes bound to the surface of the rough ER:
Proteins translated on free cytoplasmic ribosomes are head toward peroxisomes, mito, nucleus, or will remain in the cytoplasm
Proteins synthesized on the rough ER will end up either 1) secreted into the extracellular environment, 2) as integral plasma membrane proteins, or 3) in the membrane or interior of the ER, Golgi apparatus, or lysosomes (LEG acronym)
membrane bound vesicles pass b/w these three cellular compartments
Proteins synthesized on the RER are transported in vesicles that bud from the ER to the Golgi apparatus, then to the plasma membrane or lysosome

Question 10

All proteins start translation…(location)
What determines if a protein is translated on the RER or not?

The mRNA for a secreted protein encodes for a longer protein than is actually observed in the cellular exterior. Why?

Answer 10

Determined by the sequence of the protein itself
All proteins start translation in cytoplasm however, some proteins have a aa sequence in N terminal called signal sequence which is recognized by the signal recognition particle (SRP), which binds to the ribosome

Answer: The signal sequence of the protein was removed in the RER

Question 11

Integral membrane proteins

For a protein in the plasma membrane, does the portion of the protein in the ER lumen end up facing the cytoplasm or the cellular exterior?

Answer 11

Have sections of hydrophobic aa called transmembrane domains that pass through lipid bilayer membranes. The transmembrane domains are essentially signal sequences that are found in the interior of the protein (not N terminus) and they are not removed after translation
A single polypeptide can have several transmembrane domains passing back and forth through a membrane. During translation, the transmembrane domains are threaded through ER membrane, the protein is then transported in vesicles to the Golgi apparatus and plasma membrane in the same manner as a secreted protein

ends up facing the cellular exterior

Question 12

What is the default path for proteins that go through the secretory path? What consists of the secretory path? What is needed if a protein going through this path needs to go elsewhere (e.g. Golgi, the ER, the lysosome)?
What do proteins that are made in the cytoplasm

Constitutive secretory pathway
regulated secretory pathway

Answer 12

Default is plasma membrane
Secretory proteins must proceed via a specific path: from the ER to the cis Golgi to the medial and trans Golgi and from there to the cell surface
If need to go elsewhere, targeting signals are needed

Constitutive secretory pathway -> continuous or unregulated proteins secreted
regulated secretory pathway -> Specialized secretory cells (B-cells, pancreatic cells, etc.) store secretory proteins in secretory vesicles and release them only at certain times, usually in response to extracellular environment

Question 13

ALL transcription takes place in ______
ALL translation begins in _____
a. If you are a cytosolic protein, you finish translation in_______
b. However, if you are one of the following, you finish translation in _______

Answer 13

ALL transcription takes place in the nucleus
ALL translation begins in the cytosol
If you are a cytosolic protein, you finish translation in the cytosol
However, if you are one of the following, you finish translation in Rough ER
- Secreted protein
- Transmembrane protein
- Lysosomal protein
- ER/Golgi Resident Protein
(Super EG-celent Lion Tamer or LEG)
All of these proteins make signal sequence that triggers peptide complex to bring them to rough ER

Question 14

What allows the proteins ….. to finish translation in Rough ER rather than in cytosol where it started?

Answer 14

proteins = secreted protein, ER/Golgi, lysosome, transmembrane

Question 15

What happens when have mRNA of a secreted or lysosomal protein?
Co-translational translocation
What is it? What is signal sequence? What happens to the signal sequence? Why?

Answer 15

First come across mRNA and a ribosome comes across that mRNA and starts reading it at Kozak sequence
Signal sequence = signals to cytoplasmic ribosome to finish translation in Rough ER
- The signal sequence for a secreted protein is the first few aa and it is removed upon completion of protein
When use translocation pore in ER membrane and then the signal sequence embedded in the membrane (for secreted proteins) this shows how signal sequence aa are hydrophobic/nonpolar

Then protein keeps being made and while signal sequence still stuck in membrane, the protein becomes all folded up under it, inside the ER lumen
Then can package protein off and send to golgi for processing (glycosylated, sulfinated, phosphorylated) and then send it out of the cell

We have to cleave off that signal sequence bc it is stuck in ER membrane, need to cut it in order to detach the protein

Question 16

What happens when you have mRNA of membrane bound protein (First come across mRNA and a ribosome comes across that mRNA and starts reading it at….)? Where is signal sequence? What happens to signal sequence at end?
How does membrane bound protein embed in plasma membrane (which OG side of ER is facing which side of plasma membrane? Intracellular or extracellular side)?

Why is ER equivalent to/contiguous with extracellular environment?

Answer 16

First come across mRNA and a ribosome comes across that mRNA and starts reading it at Kozak sequence
Signal sequence can be anywhere in aa sequenc e, may appear several times, and remains as part of the final protein
signal recognition particles (SRP) bring whole complex (ribo, aa, mRNA) to RER ribosome docking site
We use translocation pore and do co-translational translocation, signal sequence farther along in aa sequence and still has high preference for inter-membrane region of ER bc its hydrophobic so signal sequence portions (can have more than one) will be the ones embedded in the membrane
In order to let protein go to the membrane, keep signal sequence, create vesicle with sequence in it that can travel to plasma membrane

The part of the protein that was touching the cytosol (OG intracellular environment) when embedded in membrane is still touching the cytosol

*The ER contiguous with extracellular environment bc of this process

Question 17

**Targeting signal

Answer 17

**Targeting signal:
Needed if a protein is going to stay in the secretory pathway
The default target for proteins that go through secretory path is the plasma membrane. Targeting signals are needed if a protein going through that path needs to end up elsewhere (e.g. Golgi, ER, lysosome)

Proteins that go through secretory pathway but need to stay there - ER resident proteins or some stop at golgi - and if you want your protein to stop in a certain segement of secretory pathway it’s not enough for it to have a signal sequence, it needs another sequence to tell it to stop there =

Question 18

**Localization signals

• *COMMONLY REFERED TO ON MCAT
  ex. nuclear localization signal, mitochondrial localization signal

Answer 18

Needed if protein will be sent to an organelle that is not part of the secretory pathway (nucleus, mitochondria, peroxisomes)
Targeting signal means stay in the cytosol, but there are so many places to be within the cytosol (nucleus, mito, etc.), so in order to specify where in the cytosol you want protein to stay, you need the localization signal

Question 19

What is the secretory pathway?

Answer 19

Online: The secretory pathway carries proteins to the cell surface membrane where they can be released.

Question 20

Would the following have a signal sequence, localization signal, transmembrane domain and/or targeting signal?

1) ab/Neurotransmitters/peptide hormones
2) acid hydrolases
3) enzymes for protein modificaton
4) enzymes required for lipid synthesis
5) glycolysis enzymes
6) histones, DNA/RNA, polymerase
7) PDC/Krebs cycle enzymes
8) Catalase

Answer 20

See pg. 182

Proteins for Smooth ER needs signal sequence and targeting signal

Question 21

What does the plasma membrane consist of? What is it made of?

Can CO2, O2, and steroids pass through?

Answer 21

Phospholipid (hydrophilic and hydrophobic parts), glycolipid (fatty acid groups and carb side chains also have both hydrophilic and hydrophobic parts), cholesterol
2 long hydrophobic fatty acids esterified to glycerol, and (for one type of phospholipid) charged phosphoryl choline group (choline + phosphate)
yes they can all pass bc nonpolar

Question 22

What are Integral membrane proteins?

Answer 22

embedded in membrane

Question 23

Integral membrane proteins

Answer 23

embedded in membrane (but does not cross it like a transmembrane protein)
Transmembrane domain with hydrophobic residues

Question 24

Peripheral membrane proteins

Answer 24

not embedded in the membrane at all, but stuck to integral membrane proteins, held there by hydrogen bonding and electrostatic interactions

Question 25

Fluid mosaic model

Answer 25

Mosaic of lipids and proteins are free to move back and forth fluidly but only sideways/ in two dimensions

Question 26

Molality equation (m) 
Why is this different than molarity? 

Mole fraction?

Answer 26

# moles of solute/ # kg of solvent
This is different than molarity bc molality does not change with temperature 
Since 1 liter of water = 1 kg water the molar and molal concentrations of dilute aqueous solutions are nearly the same 

Mole fraction of S = Xs = # mole of substance S/ total # moles in solution
Useful way to express concentration when more than one solute is present

Question 27

Colligative properties: what does this mean? name them and how do each of them change as add solute?

Answer 27

Number of solute particles in the solution rather than type of particle
The identity of the particle not important
We consider the effective concentration iM (i = van’t Hoff factor, M = moles)
4 colligative properties: vp, bp, fp, osmotic pressure
vp -> decrease (harder to evaporate)
bp-> increase
osmotic pressure -> increase
fp/mp -> decrease

Question 28

Vapor Pressure dependent on…
What happens to vp when the liquid contains a dissolved solute? How does vp relate to bp and adding solute to solution? What happens to bp as add solute?
Define the boiling point:

Answer 28

dependent on IMFs
higher vp means more volatile
When the liquid contains a dissolved solute this decreases vapor pressure
more energy is required to enter gas phase since the solvent molecules need to break away from their interactions with the solute before they can enter the gas phase.

bp = temp when vp=atm
At sea level atm =760 atm so solution must have 760torr to boil
but adding more solute to the same solution will decrease its vp. boiling will still take place when vp = 760atm but more heat will have to be supplied to reach this vp, so solution will boil at a higher temperature
bp increases as add solute

Question 29

What is the increase in bp directly related to?

What is bp elevation equation?

Answer 29

Increase in bp is directly related to number of particles in solution and the type of solvent
The more solute particles, the greater the bp ELEVATION, have to take into account that some molecules dissociate when dissolve

bp elevation = ΔTb = kbim
kb for water = .5 ºC/m
i = Van’t Hoff
m = molality

Question 30

Freezing point depression
What happens when we add a solute to a liquid, then try to freeze the solution? Melting point?

What is freezing point depression equation?

Answer 30

Solute particles will interfere with efficient arrangement of the solvent molecules into a solid lattice, so a liquid will be less able to achieve solid state when a solute is present and the freezing point would DECREASE
(Or, equivalently, the melting point of a solid containing a solute is decreased)

freezing point depression = ΔTf = - kfim
Kf = 1.9 ºC/m
same equation as bp elevation but negative bc temp decreasing

Question 31

**Osmosis is... (how different from diffusion) what is the only factor affects osmosis? 
Tonicity 
Isotonic
Hypertonic 
Hypotonic

Answer 31

diffusion of water from ITS high concentration to ITS low concentration, only affected by # of particles -> if electrolyte breaks up that means more particles!
- often diffusion and osmosis run in opposite directions if membrane permeable to both
Tonicity -> describe osmotic gradients but RELATE SPECIFICALLY TO THE SOLUTE
Isotonic -> solute concentration is the same inside and outside cell
Hypertonic -> solution has more total dissolved solutes than the cell (cell shrinks) (less water)
Hypotonic -> solution has less total dissolved solutes than the cell (cell explodes swollen bc water rush in) (more water)

Question 32

**What is osmotic pressure (Π)?
Equation? What is rule?
What is it affected by?

Answer 32

The pressure it would take to stop osmosis from occuring.
RULE: osmotic pressure = particle concentration

If a pressure gauge were added to the same system, osmotic pressure could be measured.

Π = MiRT  -> looks like Mirt ;) 
Π is osmotic pressure in atm
M is molarity
i is Van't Hoff factor
R is universal gas constant (0.08 L-atm/K-mol) 
T is the temperature (K) 

Osmotic pressure is only affected by the number of particles, not the identity of solute

Question 33

Passive transport and two types

For one of them there are types of proteins that help its function like…

Answer 33

Passive transport refers to any thermodynamically favorable movement of solute across a membrane, any movement down a gradient
No energy

Two types:
a) Simple diffusion -> diffusion of a solute through a membrane without help from a protein, ex steroids

b) Facilitated diffusion is the movement of a solute across a membrane, down a gradient, when the membrane itself (lipid bilayer) is. intrinsically impermeable to that solute ex. glucose
Two proteins help its function: channel proteins (ion channels) and carrier proteins which give the membrane its essential feature of selective permeability: permeable to some things despite impermeability to most things
Pores -> non-specific holes in membrane
Channels -> highly specific holes in the membrane
Porters -> undergo a conformation change to move a molecule across

Question 34

Porters: Uniports, symports, antiports

Answer 34

Porters are helper proteins for facilitated diffusion
Uniports -> transport only one molecule across the membrane to the other side
Symports -> carry two substances across a membrane in the same direction
Antiports -> carry two substances in opposite directions

Question 35

What does simple diffusion vs facilitated diffusion depend on?

Answer 35

Simple diffusion depends on SA and gradient size
Facilitated diffusion depends on a finite number of integral membrane proteins , so it exhibits saturation kinetics. Increasing the driving force for facilitated diffusion increases the rate of diffusion, but to a point, when all transport proteins become saturated
There is a Tmax (transport max) limited by the number of transport proteins you have

Question 36

Active transport is…

Primary active transport
Secondary active transport

Answer 36

Active transport is the movement of molecules against a gradient, requires energy input and always involves a protein
Primary active transport = the transport molecule is directly coupled to ATP hydrolysis
Secondary active transport = the transport molecule is not coupled directly to ATP hydrolysis, the ATP is first used to make a gradient and the potential energy in that gradient is used to drive the transport of some other molecule
ex. Glucose and sodium ions, glucose can be driven against its gradient by the cotransport of sodium ions down the sodium electrochemical gradient, previously established by ATPase, this is often seen -> the coupling with sodium gradient

Question 37

Na+/K+ ATPase:
What does it pump into and out of the cell?
Does it use E?
What else can happen to sodium and potassium/ what other transport proteins exist?
What is the purpose of Na+/K+ ATPase?
What do the charges look like in the cell?

Answer 37

Pumps 3 Na+ OUT, 2+ K IN
321 NOKIA = acronym

Hydrolyze one ATP to drive pumping

The sodium that is pumped out of the cell stays outside, since the plasma membrane is impermeable to sodium ions. But, some of the potassium ions which are pumped into the cell are able to leak back out, however, through potassium leak channels

• purpose of Na+/K+ ATPase is: a) to drive secondary active transport of many different molecules including sugars and aa,
  b) pump important to maintain osmotic balance
  c) set resting membrane potential

b Purpose cont’: Water should constantly want to enter our cells bc so many particles inside versus all water outside so you would think water would come in and make it lyse but bc of NA/K ATPase pump there are a lot of Na pumped outside so water doesn’t fly inside - maintains osmotic balance

Charge inside cell is -70mV -= resting membrane potential
RMP

Question 38

Where is the most Na+, K+, Cl-, and Ca2+?

Answer 38

The most Na+ is outside
K+ inside
Cl- outside
Ca+ outside (a lot less)

Question 39

Receptor mediated endocytosis

Answer 39

At site of receptor mediated endocytosis, receptor on outside fo cell and on inside is clathrin
Endocytosis cholesterol and whole receptor-lipoprotein complex is internalized in a vesicle called endosome
Then lipoprotein receptor is returned to cell surface

Question 40

ligand-gated ion channels

Answer 40

ex. ligand gated sodium channel
When neurotransmitter acetylcholine binds to this receptor, the receptor undergoes a conformational change and becomes an open Na+ channel. Then you get massive influx of Na+, which depolarizes cell

Question 41

Catalytic Receptors

Answer 41

have an enzymatic active site on the cytoplasmic side of the membrane
Enzyme activity is initiated by ligand binding at the extracell surface
Generally the role is that of a protein kinase, which is an enzyme that covalently attaches phosphate groups to proteins
The insulin receptor is an example of a tyrosine kinase

Question 42

**G-protein-linked receptor
ON MCAT

What is cAMP
What is Gs vs Gi?

Answer 42

Has alpha, beta, and gamma subunit inside at rest has GDP, but when something binds G protein receptor (like in this case epinephrine) so that GTP replaces GDP on alpha subunit which triggers alpha subunit + GTP to leave complex and go, for ex, to adenylyl cyclase (in some cases) and stimulate it to produce a lot of cAMP which activates cAMP-dep protein kinases, which phosphorylate enzymes and change enzyme activity in cell -> THIS IS THE LEVEL THAT YOU NEED for mcat

cAMP = secondary messenger
signal amplification
fast and temporary

Does not directly transduce its signal, but transmits it into cell with the aid of a second messenger - the most important one is cAMP (it is known as universal hunger signal bc it is the second messenger of the hormones epinephrine and glucagon, which cause energy mobilization (glycogen and fat breakdown) - get signal amplification
An epinephrine molecules activates one G-protein-linked receptor which activates many G-proteins, each G-protein activates many adenylyl cyclase enzymes, and each adenylyl cyclase makes lots cAMP from ATP, each cAMP activates many cAMP-dPK (dependent protein kinases) which phosphorylate enzymes (phosphorylation activates some and inactivates others)
end result is energy mobilization

Gs -> stimulate adenylyl cyclase
Gi -> inactivate adenylyl cyclase

Question 43

There is another G-protein linked receptor which have nothing to do with cAMP
not super high yield, just know this can happen

Answer 43

activates phospholipase C, then 2 paths -> a) make IP3 which increase intracellular Ca+ b) activate DAG which activates kinases and changes enzyme activity

Question 44

For each type of filament (in cytosketelon) state protein(s), diameter (small, medium, large), uses
Microtubule
Microfilament
Intermediate Filament

Microtubule organizing center (MTOC)
centrioles
Which is more important for mitosis?

Answer 44

Microtubule -> alpha and beta tubulin, large; mitotic spindle, intracellular transport, cilia and flagella
Microfilament -> actin, small, muscle contraction, pseudopod formation/amoeboid movement, cytokinesis (pinching the dividing parent cell into two daughter cells)
Intermediate Filament -> several diff protein types, medium, structural roles

microtubules anchored on one end by Microtubule organizing center (MTOC)
Within the MTOC is a pair of centrioles
Only MTOC is important to mitosis

Question 45

What does the cross section of cilia and flagella look like?

What is dynein?

Answer 45

Important for cilia/flagella
Dynein is a family of cytoskeletal motor proteins that move along microtubules in cells

Both cilia (ex lining respiratory track) and flagella (sperm tail) have 9 + 2 arrangement of microtubules:
9 pairs (around outside) + 2 individual in middle

Question 46

What is Dynein?

Answer 46

Each microtubule is bound to its neighbor by a contractile protein called dynein which causes movement of the filaments past one another

Question 47

Tight junctions

Occluding junctions

Answer 47

Seal lumens/separate environments

prevent things from getting into bloodstream from the intestinal lumen and prevent sepsis

Question 48

Desmosomes

Answer 48

General adhesive junctions, hold cell together

ex. Epithelial cells in skin are held together tightly but do not form a complete seal

Question 49

Gap junctions

What can go through?

Answer 49

Cell-to-cell communication
pore-like connections b/w adjactent cells
Pore big enough to transport ions, aa, carbs but not organelles or polypeptides
ex. connects heart muscle and allows ions to flow back and forth, depolarization potentials
If I get sodium influx, then you get sodium influx, and you get a sodium influx (lol like oprah)

Question 50

Name non mitosis phases and order of mitosis (M phase) components
Cell spends most time in….
What is G0?
What part is heavily regulated and where is there some regulation?

Answer 50

Interphase = G1 + S + G2
G1 = normal cell growth/activities 
S = synthesis/DNA replication 
G2 = Growth in preparation for mitosis 
M phase = includes mitosis (partitioning of cellular comp) and cytokinesis (cell division)

Cell spends most time in interphase
G0 = non-replicative, the more specialized cells like neurons, blood cells, and cells on skin surface must be replenished by stem cells

Heavy regulation before S phase and some before mitosis

Question 51

What do the chromosomes look like before and after mitosis (#, __n, ___x)? What are the phases of mitosis?
Describe the first two phases:

Answer 51

Before mitosis: 2n, 2x
After mitosis: 2n, 1x
**mnemonic: I pee on the MAT = order of cell cycle
Interphase, then mitosis: prophase, metaphase, anaphase, telophase

prophase ->

a) condense DNA
b) form mitotic spindle (book -> cell now has 2 MTOCs called asters at both ends of cell (microtubule organizing centers))
c) nuclear membrane breaks down, nucleolus disappears

genome becomes visible upon condensing into densely packed chromosomes, 46 chromosomes, 23 homologous pairs 2n (diploid, one from mom, one from dad, after DNA replication you have 2 identical strands called sister chromatids but still considered 1 chromosome) and 2x (means DNA replicated)

Metaphase:

(a) kinetochore of each sister chromosome is attached to spindle fibers that attach to MTOC at opposite pole of cell)
b) chromosomes align at the center forming metaphase plate

Question 52

Difference between homologous chromosomes and sister chromatids?

Answer 52

Sister chromatids are identical copies of a chromosome, attached to each other at the centromere. Homologous chromosomes are equivalent but nonidentical and do not come anywhere near each other during mitosis

Question 53

Second two phases of mitosis

What is the n and x value at end? End product?

Answer 53

Anaphase:

a) separate sister chromatids
b) begin cytokinesis (cleavage furrow forms)

Telophase:

a) reverse prophase -> a nuclear membrane forms around chromosomes, chromosomes de-condense, nucleolus becomes visible
b) finish cytokinesis

2n, 1x per cell (2 cells)
Two daughter cells that are IDENTICAL to each other and IDENTICAL to the parent cell

Question 54

2 types of cancer genes: oncogenes and tumor suppressor genes

What are oncogenes? Protooncogenes?

Answer 54

oncogenes = Mutated
proto-oncogenes that induce cancer, cell cycle permanently on/always active replicate so fast that no regulation, pass checkpoints in cell cycle

Proto-oncogene -> any genes that help regulate cell cycle bc potential to be cancerous if mutated, they are normal healthy cells for cell cycle
*THEY INACTIVATE CELL CYCLE
Protooncogenes -> normal versions of the genes that allow for regular growth patterns, but can be converted into oncogenes under the right circumstances (mutation, exposure to mutagen (like UV light from sun and chemicals like benzene))

Tumor suppressor genes -> either make proteins to repair DNA, halt cell cycle or promote apoptosis

Question 55

What do tumor suppressor genes do? What is p53?

Answer 55

1. Code for proteins that halt cell cycle
2. Monitor genome of cells in the cell cycle
3. If DNA, damaged, initiate DNA repair
4. If not repairable then tumor suppressor proteins trigger apoptosis
   above is all that was mentioned in class

Tumor suppressor genes produce proteins that are the inherent defense system to prevent the conversion of cells into cancer cells. The two primary means of cancer prevention a) detect damage to the genome and halt cell growth and division until the damage can be repaired, b) to trigger programmed cell death if the damage is too severe to be repaired

P53 is a produce of tumor suppressor genes when genetic damage or oncogene activity detected, it will cause apoptosis

Question 56

Apoptosis

Answer 56

allows cell to shrink and die while simultaneously minimizing damage to neighboring cells and limiting the exposure of other cells to its cytosolic contents
The death of the cell is triggered by a stressor a) external -> nitric oxide, toxin, cytokines
b) internal -> high P53 tumor suppressor protein levels
At end macrophage come to eat it

Question 57

*What are caspases? Diff types? What do they do?

Answer 57

Caspases: proteases that cleave C-terminal of an aspartic acid residue

1. Get extracellular death signal (immune cells like NK cells) and/or intracellular death signals
2. Initiator caspases
3. Effector caspases

responsible for carrying out the events of apoptosis
They have cysteines inactive site and cleave their target proteins at aspartic acid sites, hence name c-asp-ases
Like all potentially damaging enzymes, are produced in their inactive form as procaspases (zymogen)
there is cluster of them that causes a cascade of activation
Initiator caspases respond to extra and intra cellular death signals by clustering together which allows them to activate each other

Question 58

Oxidative stress: what is it due to, what can it cause?

Answer 58

Oxidative stress can be due to increased levels of peroxides or free oxygen, which then generated radicals which can damage DNA, cell proteins, and lipid bilayers
Oxidative stress is linked to cancer bc can allow oncogenes to become active
Oxidative stress is also natural part of immune system due to phagocytes so we need to find balance

Question 59

FasL

Answer 59

a death receptor ligand

Question 60

What is southern blot used on? Western?

Answer 60

Southern blot used to study DNA, not proteins

Western blot for proteins

Question 61

Components of cell membrane
outer/inner leaflet
Imagine a protein in the lipid bilayer, what is it made of?

Answer 61

phospholipid, cholesterol, proteins, carbs
outer/inner leaflet -> inside or outside-facing part of membrane
Protein in lipid bilayer is made of signal sequence

Question 62

Simple diffusion works for….
examples?

Facilitated diffusion works for…
examples?

Answer 62

Works well for small, hydrophobic molecules
ex. CO2, O2, steroids

polar and charged molecules, such as carbohydrates, glucose, amino acids, nucleosides, H2O and ions, to cross the plasma membrane.

Question 63

Agonst vs antogonist

Analogue

Answer 63

Agonst -> an analogue that binds receptor and leads to drug action/effect
Antagonist -> an analogue that binds to receptor and leads to no drug action/effect

Question 64

Are the following “gain of function” mutations or “loss of function” mutations?
Oncogenes
Tumor suppressor genes

Answer 64

Oncogenes -> gain of function mutation bc gained ability to divide w/o control
Tumor suppressor genes -> loss of function mutation bc loss of ability to halt the cell cycle and repair

Question 65

Retrograde

Answer 65

means backward

so may mean the same mxn but in reverse