Reading 3: Cell Structures

Question 1

Define phospholipid bilayer

Answer 1

forms the basic structure of the plasma membrane

Question 2

What does each phospholipid consist of?

Answer 2

a glycerol backbone with two fatty acid tails on one side and a phosphate head group

Question 3

amphipathic

Answer 3

Molecules with both polar an non polar regions

Question 4

Hydrophilic

Answer 4

Polar

Question 5

Hydrophobic

Answer 5

Non-polar

Question 6

Transmembrane (integral) proteins participate what kind of functions

Answer 6

molecular transport, cell adhesion, cell-cell recognition, signal transduction, and enzymatic activity

Question 7

Plasma membrane protein classifications

Answer 7

Transmembrane and peripheral

Question 8

Where are peripheral proteins located?

Answer 8

the edge, or periphery, of the membrane.

Question 9

Another word for edge

Answer 9

periphery

Question 10

How do peripheral proteins interact with the membrane ?

Answer 10

by reversibly interacting with the polar head group of phospholipids, or by permanently embedding into the bilayer using a glycosylphosphatidylinositol (GPI) anchor

Question 11

How do peripheral protiens function?

Answer 11

as accessories in signal transduction, enzymatic activity or cell adhesion processes.

Question 12

what is the function of cholesterol within the membrane?

Answer 12

regulating membrane fluidity

Question 13

What is the fluid mosaic model?

Answer 13

the phospholipids, membrane proteins, and cholesterol molecules are constantly in motion as they maintain the bilayer structure, similar to the movement of sailboats bobbing in the ocean.

Question 14

transverse migration

Answer 14

membrane components spontaneously flip from one side of the bilayer to the other

Question 15

In the case of transverse migration what enzymes become active?

Answer 15

flippase, floppase, and scramblase

Question 16

Why is transverse migration not ideal?

Answer 16

flipping to the other side of the bilayer would cause the polar head group to intermix briefly with the nonpolar fatty acid tails, this movement is thermodynamically unfavorable

Question 17

What is the basic structure of a plasma membrane?

Answer 17

phospholipid bilayer, carbohydrates, and cholesterol

Question 18

How do membrane components move within the membrane?

Answer 18

rotate clockwise or counterclockwise and move laterally from side to side or front to back

Question 19

What determines membrane fluidity?

Answer 19

Temperature, saturation, cholesterol

Question 20

As temperature rises what happens to the phospholipid?

Answer 20

Speeds up the movement of the phospholipid bilayer, and the hydrophobic interactions between the fatty acid tails are disrupted.

Question 21

As temperature rises what happens to the membrane fluidity?

Answer 21

membrane fluidity to increase and, thus, weakens the membrane structure

Question 22

As temperature drops what happens to the phospholipid?

Answer 22

slows movement of the phospholipid bilayer, enhancing the association between membrane phospholipids.

Question 23

As temperature drops what happens to the membrane fluidity?

Answer 23

membrane becomes more rigid

Question 24

Saturated fatty acid tails causes what?

Answer 24

a crowding effect minimizes movement and causes a rigid phenotype

Question 25

Unsaturated fatty acid tails causes what?

Answer 25

the membrane becomes more fluid due to the “kinked” structure of the tail, which arises from the presence of one or more double bonds.

Question 26

How do cells regulate membrane fluidity?

Answer 26

modifying the ratio of saturated to unsaturated phospholipids.

Question 27

what is the main regulator of membrane fluidity

Answer 27

cholesterol

Question 28

At standard temperatures, such as body temperature, increased cholesterol causes

Answer 28

a reduction in membrane fluidity by packing between the “kinked” fatty acid tail structures of unsaturated phospholipids

Question 29

Low temperatures with increased cholesterol causes

Answer 29

cholesterol actually serves as a spacer between phospholipids to prevent solidification of the membrane

Question 30

Define Lipid rafts

Answer 30

are localized regions of the plasma membrane that contain a specialized collection of membrane proteins that work together to carry out cellular signaling

Question 31

central dogma of genetics

Answer 31

cell types are programmed to express only a particular subset of genes

Question 32

define chromatin

Answer 32

DNA's relaxed, uncoiled organizational state

Question 33

define heterochromatin

Answer 33

DNA that is tightly coiled

Question 34

What is the function of heterochromatin?

Answer 34

protects genes that are not to be actively used and prevents gene expression

Question 35

define euchromatin

Answer 35

DNA in a more relaxed conformation

Question 36

What is the function of euchromatin?

Answer 36

permits access to genes for transcription

Question 37

define chromosome

Answer 37

condensed supercoiled DNA for the mitotic phase

Question 38

what is the de novo gene expression signal?

Answer 38

A signal to make brand new proteins from scratch

Question 39

transcription factors

Answer 39

Proteins that bind to promoters and initiate RNA transcription

Question 40

promoter regions

Answer 40

initiating site for RNA transcription

Question 41

the transcription process

Answer 41

activate transcription factors, bind to specific promoter regions

Question 42

pre-mRNA transcript contains

Answer 42

a combination of introns and exons

Question 43

Introns

Answer 43

non coding regions of the genome

Question 44

alternative splicing

Answer 44

certain exons are retained and others are spliced out

Question 45

How can we protect the mRNA from degradation

Answer 45

add a 5’ cap, and polyadenylation

Question 46

What is the process of polyadenylation

Answer 46

adds ~100-200 adenine (A) nucleotides to its 3’ end

Question 47

poly-A tail

Answer 47

3' end

Question 48

Why do we want to slow enzymatic degradation of the mRNA transcript

Answer 48

allowing sufficient time for protein translation before the mRNA degrades.