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

Lecture 5: Membrane Structure, Part I 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
Selective permeability
selective passage of molecules and ions into and out of the cell
21
What types of molecules can rapidly diffuse across the plasma membrane?
Small, nonpolar molecules
22
What types of molecules diffuse slowly across the plasma membrane?
Large polar, charged molecules
23
How do molecules that diffuse slowly (or not at all) cross the plasma membrane without diffusion?
Facilitated diffusion as molecules are assisted by specialized transport proteins in the membrane Ex. glucose
24
Both ___ and ____ are composed of lipid bilayer
plasma and internal membrane
25
Lipid bilayer composition
Consists of nonpolar (hydrophobic) membrane composed of 2 layers of lipid molecules, cholesterol, and various membrane proteins
25
Fatty acid
building blocks of membrane lipids
26
Chemical structure of fatty acid
Amphipathic Hydrophilic polar head Hydrophobic nonpolar tail
27
Membrane lipids
composed of modified fatty acids in plasma or internal membrane 1 fatty acid hydrophilic head 2 fatty acid hydrophobic tails
28
Why are fatty acids ideal component for cell membrane
can interact with both aqueous and nonaqueous environments
29
What are common type of membrane lipids in cell membrane
Phospholipids
30
Phospholipid composition
Have hydrophilic phosphate group in the head and two hydrophobic tails
31
Why are phospholipids energetically favorable?
Energetically favorable for hydrophilic heads to contact water and hydrophobic tails to avoid contact with water and aggregate with each other
32
What is issue when phospholipids form sheets?
edges are exposed, exposure of hydrophobic molecules to hydrophilic environment
33
What does the sheet spontaneously form a sphere?
sealed compartment so hydrophobic tails at edge do not contact water
34
What is on both sides of lipid bilayer?
Aqueous environment
35
Lateral diffusion
common movement of lipids move within plane of lipid bilayer
36
Flip flop movement
phospholipids move from one monolayer to another without help of proteins and is energetically unfavorable
37
Membrane fluidity
Lateral diffusion of membrane lipids and depends on the composition of lipid bilayer
38
Do all membranes must be fluid?
Yes; always occuring
39
Membrane fluidity is determined by
Packing of hydrocarbon tails in lipid bilayer Length of hydrocarbon tails Number of Double Bonds Cholesterol Temperature
40
Packing of hydrocarbon tails in lipid bilayer on membrane fluidity
More fluid: loose packing of tails as trying to minimize all hydrophobic interactions Less fluid: close packing of tails
41
Length of hydrocarbon tails on membrane fluidity
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
Number of double bonds on membrane fluidity
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
At room temperature, how does cholesterol influence membrane fluidity
Less cholesterol at room temp increases fluidity More cholesterol at room temp decreases fluidity
44
Melting temperature (Tm)
temperature where membrane transitions from crystal like state to fluid like state
45
At low temp, how does cholesterol impact fluidity
Increase cholesterol, increases fluidity Prevents phospholipids tails from packing too tightly
46
How do phospholipids affect the Tm?
through composition and length
47
At high temp, how does cholesterol impact fluidity
Increase cholesterol, decrease fluidity Restrains movement
48
Why is maintaining a fluid membrane important?
Need fluid membrane for allowing proper functioning of the cell and movement of essential molecules across the membrane
49
Transmembrane Proteins
Extend through lipid bilayer Have hydrophilic and hydrophobic regions (amphipathic) Made of alpha helices Can be single pas or multi pass
50
What are the 2 challenges for Transmembrane proteins?
1. Many amino acids are hydrophilic (50%) Cause issues as they do not want to be in hydrophobic interior 2. 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
How do transmembrane proteins overcome the 2 challenges?
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
Single Pass transmembrane proteins
Only require 1 alpha helix to pass through lipid bilayer
52
Why are the strategies important for transmembrane proteins?
Create stable structure in nonpolar environment
53
To help protein channels pass important molecules through, they can use
polar amino acids on multipass proteins
54
What does the number of transmembrane segments say about a protein?
Number provides information about function of protein
54
Multipass transmembrane segments alpha helices use amino acids to create
hydrophilic pore In one turn of alpha helix, 3 are nonpolar and 1 are polar
54
Multipass transmembrane proteins
Require multiple alpha helices to pass through lipid bilayer
55
Transmembrane Segment
20 nonpolar amino acids in protein used to pass through lipid bilayer Can have polar uncharged, but NO POLAR CHARGED
56
+ score in hydrophobicity plot =
hydrophobic amino acid
57
negative - score in hydrophobicity plot =
hydrophilic amino acid
58
Kyte and Doolittle numerical scale of hydrophobicity plot
Transmembrane segments have value of more than 1.6 and are more than 20 amino acids long
59
Glycosylation
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
Glycocalyx or cell coat
carbohydrate layer on plasma membrane from glycosylated proteins and lipids; protect cells against mechanical and chemical damage
61
Glycolipid
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
Where does glycosylation occur?
ER and Golgi apparatus
63
How is glycosylation is established and maintained
made in golgi and ER --> enter transport vesicle --> goes to extracellular environment Never touches cytosol

Cell Biology (13 decks)

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