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Cell Biology > Lecture 5: Membrane Structure, Part I > Flashcards

Lecture 5: Membrane Structure, Part I Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Prokaryotic Cell

A

Small, unicellular
DNA in cytoplasm
One circular chromosome
No organelles
Oldest cell type

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2
Q

Eukaryotic Cell

A

Large cells, diverse shapes and functions
Unicellular or multicellular
DNA is in nucleus
Multiple linear chromosomes
Several organelles
Evolved from prokaryotes

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3
Q

What is an organelle?

A

membrane bound structures in cell that performs specialized functions

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3
Q

Similarities between prokaryotic and eukaryotic cells

A

Both have DNA, ribosomes, cytoplasm, and plasma membrane

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4
Q

Do prokaryotic and eukaryotic cells have organelles?

A

Only eukaryotic

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5
Q

Endoplasmic Reticulum (ER)

A

membrane of enclosed sacs that produces components of plasma membrane (proteins and lipids) and material secreted by the cell

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5
Q

Nuclear envelope

A

Double membrane surrounding nucleus which works with nuclear pores to regulates entry of only allowing specialized proteins and molecules

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5
Q

Nucleus

A

Prominent organelle in a eukaryotic cell and contains linear chromosomes
Can be observed by light and electron microscopes
Enclosed by nuclear envelope
Surrounded by lipid bilayer

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6
Q

2 Membranes of Nuclear Envelope

A

Outer membrane: in contact with cytoplasm

Inner membrane: in contact with chromosomes

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6
Q

Nuclear pores

A

Small channel embedded within nuclear envelope which acts a getaway for molecules to move between nucleus and cytoplasm of a cell
Allows selective transport of materials

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7
Q

What is the association between the endoplasmic reticulum (ER) and the nuclear envelope?

A

Membranes of ER are continuous with outer membrane of nuclear envelope

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8
Q

Rough ER

A

has ribosomes for protein synthesis → near nucleus

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9
Q

Smooth ER

A

no ribosomes and important for lipid synthesis → far away from nucleus and close to plasma membrane since made out of lipids

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10
Q

Describe the association between the ER and the Golgi apparatus.

A

Works together
Proteins synthesized in ER and other molecules from ER are packaged into transport vesicles and enter golgi apparatus

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11
Q

Golgi Apparatus

A

stacks of membrane enclosed sacs that receive molecules in ER and and directs them to various locations within the cell

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12
Q

What happens when proteins traveling from cis to trans face of Golgi apparatus?

A

Proteins undergo processing and protein modification in stacks (cisternae)

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13
Q

Cis face of Golgi apparatus

A

Proteins enter from ER
Side nearest ER and facing nucleus

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14
Q

Trans face

A

exit side, where modified molecules are packaged into vesicles and sent to final destination within the cell

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15
Q

What is common destination of when proteins leave the Golgi Apparatus

A

Lysosomes

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16
Q

Lysosomes

A

irregularly shaped organelles that contain enzymes used to digest macromolecules

Have various hydrolytic enzymes (hydrolysases) that can degrade different macromolecules

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17
Q

Molecules that are degraded by lysosomes are often

A

Recycled

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18
Q

All living cells must have

A

plasma membrane

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19
Q

Plasma membrane

A

Defines boundary of cell and separates cytosol from extracellular environment
Has selectively permeability

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19
Q

Internal membrane

A

Form organelles
Provide cell with intracellular compartments to perform specific functions

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20
Q

Selective permeability

A

selective passage of molecules and ions into and out of the cell

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21
Q

What types of molecules can rapidly diffuse across the plasma membrane?

A

Small, nonpolar molecules

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22
Q

What types of molecules diffuse slowly across the plasma membrane?

A

Large polar, charged molecules

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23
Q

How do molecules that diffuse slowly (or not at all) cross the plasma membrane without diffusion?

A

Facilitated diffusion as molecules are assisted by specialized transport proteins in the membrane
Ex. glucose

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24
Q

Both ___ and ____ are composed of lipid bilayer

A

plasma and internal membrane

25
Q

Lipid bilayer composition

A

Consists of nonpolar (hydrophobic) membrane composed of 2 layers of lipid molecules, cholesterol, and various membrane proteins

25
Q

Fatty acid

A

building blocks of membrane lipids

26
Q

Chemical structure of fatty acid

A

Amphipathic
Hydrophilic polar head
Hydrophobic nonpolar tail

27
Q

Membrane lipids

A

composed of modified fatty acids in plasma or internal membrane

1 fatty acid hydrophilic head
2 fatty acid hydrophobic tails

28
Q

Why are fatty acids ideal component for cell membrane

A

can interact with both aqueous and nonaqueous environments

29
Q

What are common type of membrane lipids in cell membrane

A

Phospholipids

30
Q

Phospholipid composition

A

Have hydrophilic phosphate group in the head and two hydrophobic tails

31
Q

Why are phospholipids energetically favorable?

A

Energetically favorable for hydrophilic heads to contact water and hydrophobic tails to avoid contact with water and aggregate with each other

32
Q

What is issue when phospholipids form sheets?

A

edges are exposed, exposure of hydrophobic molecules to hydrophilic environment

33
Q

What does the sheet spontaneously form a sphere?

A

sealed compartment so hydrophobic tails at edge do not contact water

34
Q

What is on both sides of lipid bilayer?

A

Aqueous environment

35
Q

Lateral diffusion

A

common movement of lipids move within plane of lipid bilayer

36
Q

Flip flop movement

A

phospholipids move from one monolayer to another without help of proteins and is energetically unfavorable

37
Q

Membrane fluidity

A

Lateral diffusion of membrane lipids and depends on the composition of lipid bilayer

38
Q

Do all membranes must be fluid?

A

Yes; always occuring

39
Q

Membrane fluidity is determined by

A

Packing of hydrocarbon tails in lipid bilayer
Length of hydrocarbon tails
Number of Double Bonds
Cholesterol
Temperature

40
Q

Packing of hydrocarbon tails in lipid bilayer on membrane fluidity

A

More fluid: loose packing of tails as trying to minimize all hydrophobic interactions
Less fluid: close packing of tails

41
Q

Length of hydrocarbon tails on membrane fluidity

A

More fluid: short tail for less interaction between tails
Less fluid: long tail for more interaction between tails, more carbons = more hydrophobic interactions for less fluidity

42
Q

Number of double bonds on membrane fluidity

A

More fluid: Unsaturated: one or more double bonds as there is less interaction between tails and bend to have more movement (liquid at room temp)
Less fluid: Saturated: no double bonds as more interaction between tails and very straight structure to engage in more hydrophobic interactions (solid at room temp)

43
Q

At room temperature, how does cholesterol influence membrane fluidity

A

Less cholesterol at room temp increases fluidity
More cholesterol at room temp decreases fluidity

44
Q

Melting temperature (Tm)

A

temperature where membrane transitions
from crystal like state to fluid like state

45
Q

At low temp, how does cholesterol impact fluidity

A

Increase cholesterol, increases fluidity
Prevents phospholipids tails from packing too tightly

46
Q

How do phospholipids affect the Tm?

A

through composition and length

47
Q

At high temp, how does cholesterol impact fluidity

A

Increase cholesterol, decrease fluidity
Restrains movement

48
Q

Why is maintaining a fluid membrane important?

A

Need fluid membrane for allowing proper functioning of the cell and movement of essential molecules across the membrane

49
Q

Transmembrane Proteins

A

Extend through lipid bilayer
Have hydrophilic and hydrophobic regions (amphipathic)
Made of alpha helices
Can be single pas or multi pass

50
Q

What are the 2 challenges for Transmembrane proteins?

A
  1. Many amino acids are hydrophilic (50%)

Cause issues as they do not want to be in hydrophobic interior

  1. Peptide bonds that connect amino acids in a protein have polar bonds causing partial charges

Partial charges and hydrophobic environments do not get along

51
Q

How do transmembrane proteins overcome the 2 challenges?

A
  1. Use lots of nonpolar hydrophobic amino acids within transmembrane segments
  2. Put nonpolar amino acids in alpha helix

Provides stable structure being stabilized by H bonds and neutralizes partial charges

52
Q

Single Pass transmembrane proteins

A

Only require 1 alpha helix to pass through lipid bilayer

52
Q

Why are the strategies important for transmembrane proteins?

A

Create stable structure in nonpolar environment

53
Q

To help protein channels pass important molecules through, they can use

A

polar amino acids on multipass proteins

54
Q

What does the number of transmembrane segments say about a protein?

A

Number provides information about function of protein

54
Q

Multipass transmembrane segments alpha helices use amino acids to create

A

hydrophilic pore

In one turn of alpha helix, 3 are nonpolar and 1 are polar

54
Q

Multipass transmembrane proteins

A

Require multiple alpha helices to pass through lipid bilayer

55
Q

Transmembrane Segment

A

20 nonpolar amino acids in protein used to pass through lipid bilayer

Can have polar uncharged, but NO POLAR CHARGED

56
Q

+ score in hydrophobicity plot =

A

hydrophobic amino acid

57
Q

negative - score in hydrophobicity plot =

A

hydrophilic amino acid

58
Q

Kyte and Doolittle numerical scale of hydrophobicity plot

A

Transmembrane segments have value of more than 1.6 and are more than 20 amino acids long

59
Q

Glycosylation

A

sugars attached to another molecule (lipid or protein)
Occurs in ER and Golgi
Occurs on non cytosolic side
Never exposed to cytoplasm
Sugars are made outside the cell

60
Q

Glycocalyx or cell coat

A

carbohydrate layer on plasma membrane from glycosylated proteins and lipids; protect cells against mechanical and chemical damage

61
Q

Glycolipid

A

Lipid + sugar
Acquire sugar groups in golgi and are always on non cytosolic face of membrane
Once lipids get glycosylated → cause symmetry
Never touch cytosol

62
Q

Where does glycosylation occur?

A

ER and Golgi apparatus

63
Q

How is glycosylation is established and maintained

A

made in golgi and ER –> enter transport vesicle –> goes to extracellular environment
Never touches cytosol

Cell Biology (13 decks)

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