Block 1 Content

Why is it so hard to say precisely how many cell types there are?

Cells exist on a continuum; they are constantly adapting to their environment and changing fxn in accordance to what is needed

What is homeostasis?

The self-regulating process by which biological conditions maintain stability in a changing external environment

• Physiological homeostasis is very energetically expensive; does not exist at equilibrium

What is cell theory?

The theory that states

• all living things are made of cells

• cells are the functional units of life

• all cells are made of roughly the same material

  • all energy flows of life occur within cells

Why is it important for cells to be able to communicate? And how (basics)?

To form complex tissues for higher purpose;

• sense and responding to other cells

• coordinate actions

• develop specialized functions

Endocrine communication

Signals traveling through the blood stream via hormones

Paracrine

Signaling from one cell to an adjacent cell via released chemicals

Autocrine

Signaling from one cell to itself, perhaps on another region of the same cell

What would happen if the plasma membrane were to stop functioning?

Materials would be able to pass through unfiltered; cells would not be able to signal properly

What would happen if the nucleus membrane were to stop functioning?

halting of gene expression/transcription

What would happen if the mitochondria were to stop functioning?

Inability to undero aerobic respiration/ no ATP

What would happen if the ribosomes were to stop functioning?

proteins would not be able to synthesize or translate

What would happen if the golgi apparatus were to stop functioning?

proteins and lipids would not be sorted and packaged for delivery— lack of proteins or lipids being transported

What would happen if the lysosomes were to stop functioning?

Buildup of damaged cellular material; if broken, then hydrolytic enzymes would kill the cell

What would happen if the peroxisomes were to stop functioning?

buildup of fatty acids

Describe the basic structure of a phospholipid (as seen in the bilayer)

Hydrophilic head (glycerol backbone) + hydrophobic tails (fatty acid chains); heads face outward to the aqueous environment and the tails face inward

What are integral proteins?

Proteins embedded in the membrane bilayer; they are amphipathic with portions inside and outside of the bilayer

What are peripheral proteins?

Non-covalently bonded with integral proteins; they are proteins only on the outside (extracellular) of the cell

• Can help signal to the integral proteins

List the three important lipid bilayer components. Why is it important to know there are many components?

• Phospholipids

• Sphingolipids

• Cholesterol

To understand that there are different structural components of the plasma membrane and that they have different functions.

How can phospholipids allow for specificity?

They have different polar functional regions atop the glycerol head

What effect does cholesterol have on the membrane and why?

Cholesterol is similarly shaped to a phospholipid; it is amphipathic with a long-chain fatty tail— more fatty acid chains → more rigid

• Therefore, cholesterol contributes to the rigidity of the cell membrane

What effect might longer lipid tails have on the plasma membrane?

Longer + thicker → more rigid/saturated

If the plasma membrane had fewer saturated fatty acids and more unsaturated fatty acids, the plasma membrane would…

• be more fluid

• allow for more movement of integral proteins

About how thick is the lipid portion of the bilayer?

5-6 nm

T/F: The intracellular matrix anchors the cell to its place, and the extracellular matrix is responsible for upkeep communication

False. The extracellular matrix is responsible for both of those things.

Describe the relative concentrations of ions inside and outside of a cell? (Na⁺, K⁺, Cl^-, Ca²⁺)

Na: High outside, low inside

K+: Low outside, high inside

Cl: High outside, low inside

Ca: High outside, low inside

What unit do we use to measure the diameter of a cell? What about the width of the bilayer?

microns; nanometers

What is the role of the Na+/K+ ATPase?

Develop and maintain steady-state ion gradients for ALL cells

What are the two major parameters that determine the resting membrane potential?

1. Ion gradients

2. Membrane permeability

What is the consequence of having K+ leak channels?

Potassium is constantly leaking out from cells, creating a negative cell interior

What is the typical range of the resting potential?

-50 to -100 mV (~-82 mV)

What is the major determinant of the membrane potential?

The equilibrium potential of potassium because K+ leak channels are almost always open (free permeability)

T/F: The membrane potential shifts toward the equilibrium potential of whichever ion the membrane is most permeable to

True

When Na+ channels are open…

the membrane potential depolarizes (becomes more positive/less negative) because the equilibrium potential for Na+ is positive (~+64 mV)

When K+ channels are open…

the membrane potential hyperpolarizes (becomes more negative) because the equilibrium potential for K+ is negative (~-92 mV)

What is the Nernst equation?

A formula for the membrane potential when a specific ion is at theoretical equilibrium (when chemical and electrical forces are equal)

• Aka the formula for the equilibrium potential for a specific ion

• V = -60 * log([K⁺]_in/[K⁺]_out)

What is the Goldman equation?

A formula for the membrane potential that considers ALL ions and:

1. Na+ and Cl- ions are also contributing to the membrane potential

2. Ion permeabilities determine the influence of each ion on the membrane potential

What is the ratio between Na+ and K+ entering and exiting the cell?

3 Na leaving; 2 K entering

T/F: Different cells have different permeabilities of ions

Yes; this allows for different functions (e.g. muscle cells are more permeable to Cl-)

What are the three types of gated ion channels? What triggers their opening?

1. Voltage-gated channels: opened by depolarization

2. Ligand-gated channels: opened by a signaling molecule that binds to channel protein

3. Mechanically-gated channels: open when channels get stretched

What is the concept of a graded potential?

The idea that the size of voltage response varies with the strength of the stimulus

• Additivity: you can couple multiple stimuli of the same type to produce a greater response; you can couple opposite stimuli to cancel each other out

List events of an action potential

1. Stimulus

2. small depolarization to threshold

3. Na+ channels open, Na+ influx, HUGE depolarization

4. Na+ channels spontaneously close

5. K+ voltage gated channels open, K+ efflux

6. Repolarization

7. Hyperpolarization

8. Return to resting membrane potential

What are the refractory periods? What can they tell us?

Absolute refractory period: Around the peak of the depolarization, the Na+ channels need to reset and you cannot trigger another action potential no matter what

Relative refractory period: Around the repolarization phase and after, the K+ channels need to reset and you can trigger another action potential only if the stimulus is STRONG

• Refractory periods influence the max rate of action potentials and the characteristics of AP propagation

What are the two factors that influence the velocity of an action potential?

1. Diameter of the axon: increased diameter → less resistance → faster signals

2. Myelination: More myelin increases velocity (kinda like lube for the axon)

What cell produces myelin?

Schwann cells

What part of the axon actually allows for the initiation of an action potential?

Nodes of Ranvier because they allow for exposure to the extracellular side for influx of Na+

How does Na+ influx influence local depolarization?

influx of Na+ depolarizes the local axon and opens the ion channels at the next node of Ranvier

Why does it make sense that the K+ equilibrium potential is -?

Because it wants to efflux due to its chemical gradient which would result in a loss of + ions

Why does it make sense that the Na+ equilibrium potential is +?

Because it wants to influx due to its chemical gradient which would result in a gain of + ions

What is the dispersed form of DNA called?

Chromatin

This protein acts as a spool for nucleic acids?

Histones

What are nucleic acids made of?

Pentose sugars and phosphates

What are the three constituents of DNA

1. Deoxyribose sugars

2. Phosphate

3. Base groups (AT, CG)

Nucleoside

Base + sugar

nucleotide

Nucleoside + phosphate

(base + sugar + phosphate)

What are the purines? And the pyrimidines?

Purines: Adenosine, Guanine

Pyrimidines: Cytosine, Uracil, Thymine

What protein carries out transcription (the synthesis of the RNA strand)?

RNA polymerase

Promoter region

Region of the RNA strand that initiates transcription

DNA is read in the ______ direction and RNA is made in the _____ direction

3’ → 5’

5’ → 3’

(complementary)

RNA splicing

splicing out portions of the DNA gene to be or not to be copied

• Introns: portions of the gene omitted

• Exons: portions of the gene read and copied

Which is more stable: RNA or DNA?

DNA is more stable than RNA.

• DNA is more resistant to hydrolysis

• (Could this allow for splicing?)

T/F: DNA in all of your cells is the same

True

What is the promoter in DNA?

A sequence "upstream” to the start of a gene to which RNA polymerase binds

What are the transcription factors in DNA?

Proteins that bind to the promoter to augment binding to RNA polymerase

What are the steps of transcription?

0. Unwind chromatin and nucleosomes

1. Initiation: proteins bind to DNA to tell RNA Polymerase to begin transcribing

2. Elongation and strand separation: strands elongate to allow for transcription of the DNA strand

3. Termination: Specific DNA sequence that tells RNA polymerase to stop transcribing

Where does translation occur?

Cytoplasm

What are codons and anticodons?

Codons are the 3-letter (base) codes that code for amino acids on the mRNA strand

Anticodons are the complementary codons on the tRNA that allow it to bind to the mRNA strand

How are amino acids linked?

Via covalent peptide bonds

T/F: There are control points at the start and end of transcription/translation

False, there are control points after every step in transcription/translation

T/F: Proteins are being turned over all of the time at different rates

True. (Turned over being synthesized and degraded)

What is the half-life of a protein? Do they vary?

The interval required for the quantity of protein remaining to halve; yes, they vary depending on the functionality of the protein

What are the two organelles responsible for proteolysis?

1. Lysosomes

2. Proteosomes

Lysosomes

Lipid membrane-bound compartments that contain various hydrolases + proteases

• The internal pH is very low

• Use endocytosis to degrade material

• Identify monoubiquinated proteins to degrade

Proteosomes

Proteolytic machines that line the inside of cylindrical chambers to create the proteolysis site

• Degrade abnormal and misfolded proteins (sometimes antigens)

• Identify polyubiquitinated proteins to degrade

What organelle tags proteins with ubiquitin for destruction? HINT: This organelle also directs them to their final activation location

Golgi apparatus

What is the V-ATPase?

The vacuolar ATPase shifts protons (H+) into lysosomes and endosomes to maintain a low pH

What is/ what are the steps of autophagy?

Autophagy is the mechanism for disposing of large particles via autophagosomes

1. Envelopment

2. Sealing

3. Merging w/ Lysosomes → release lysosome interior content into the cell for hydrolysis

4. Result in residual body

What is crinophagy?

The process for degrading secretory proteins (e.g. hormones) that have gone beyond their “shelf life”

• lysosomes fuse with the old secretory vesicles and degrade their content

How are proteasomes regulated?

There are regulatory complexes that guard the opening of the cylindrical chamber that allow access only to selected, unfolded, proteins

What can you tell me about the EI, E2, E3 pathway?

It is a hierarchical structure that keeps adding ubiquitin to proteins to direct them to their specific slaughterhouse (lysosomes or proteasomes)