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Malika Biochem MCAT > Chapter 5 & 8 > Flashcards

Chapter 5 & 8 Flashcards

1
Q

What are general functions of the plasma membrane?

A

Provide a selectively permeable barrier, transport solutes in and out of membrane, bind ligands to communicate extracellular cell signals and regulate interactions between cells

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2
Q

What are the three dynamic properties of the cell membrane?

A

Movement, division, fusion

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3
Q

What does the fluid-mosaic model say about the plasma membrane?

A

Describes function:
-Main function is to transport solutes in and out of membrane and maintain permeability
Describes fluidity:
-It says that phospholipids are free to move within the bilayer
Describes structure:
-There are two opposite facing leaflets that contain polar heads and an inner leaflet that contains hydrophobic tails
- There are also integral proteins embedded in the membrane and peripheral proteins loosely associated with the membrane on the outside and inside of the cell

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4
Q

How do cell plasma membranes vary across different cells in the body?

A

Different cells contain different composition of their plasma membrane. For example, the ratio of lipid to protein varies depending on the type of cell membrane.

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5
Q

What kinds of molecules make up the plasma membrane?

A

The majority are phospholipids, then fatty acids, triacylglycerols, steroids, cholesterol, sphingolipids, and waxes.

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6
Q

What are the two types of passive transport across the cell membrane?

A

Simple diffusion and facilitated diffusion

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7
Q

What is simple diffusion?

A

It’s when a substance moves from an area of high concentration to an area of low concentration, directly through the semipermeable membrane without assistance of other proteins. All nonpolar molecules like carbon dioxide & O2 can diffuse freely through membrane. Even big nonpolar molecules.

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8
Q

What is facilitated diffusion??

A

When a substance moves from an area of high concentration to an area of low concentration, with the help of a membrane protein such as a channel protein or carrier protein.
-charged and POLAR substances use this method of passive transport.

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9
Q

What are the three types of facilitated diffusion?

A

Ungated channel, voltage-gated channel, ligand-gated channel

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10
Q

Ungated facilitated diffusion

A

There is no regulation required here, the molecule merely travels through the protein channel. An example is potassium leak channel which contributes to the negative resting membrane potential of the cell.

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11
Q

Voltage gated facilitated diffusion

A

The protein channel that allows the molecule to pass through is activated and deactivated by the membrane potential change. For example, depolarization of the membrane causes sodium channels to open and sodium to rush into the cell.

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12
Q

Ligand gated facilitated diffusion

A

This involves the binding of a ligand which causes the protein channel to open or close. An example is a Cl- channel which activates when the neurotransmitter GABA binds to it, causing hyper polarization of the cell.

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13
Q

What are lipid rafts?

A

A collection of similar lipids clustered, and regions of the membrane that serves as attachment points for other signaling biomolecules. Contain a lot of cholesterol in them. They don’t travel as fast as single phospholipids throughout the membrane.

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14
Q

What are micelles?

A

Closed lipid monolayers with fatty acids tails pointing towards the middle and the polar head groups on the outside.

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15
Q

What are liposomes?

A

Donut shaped lipid bilayer. Hydrophilic heads on the outside layer and innnermost layer both pointing to aqueous solution. Inside of the donut has hydrophobic fatty acid tails.

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16
Q

Describe the two uncatalyzed movements of phospholipids in the membrane.

A
  1. Lateral diffusion - phospholipids diffuse across the cell membrane within one leaflet moving up/down and side to side. This movement is fast and common.
  2. Flip-flop trans-bilayer diffusion - phospholipids move between two membrane leaflets. This movement is very slow and rare.
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17
Q

Describe the catalyzed movement of phospholipids in the membrane that uses ATP.

A

Using ATP, the flippase enzyme flips the phospholipid from the outer leaflet to inner leaflet. The floppase enzyme flips the phospholipid from the inner leaflet to the outer leaflet.

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18
Q

Describe the catalyzed movement of phospholipids in the membrane that doesn’t use ATP.

A

The scramblase enzyme, which doesn’t use ATP flips one phospholipid in one direction and another phospholipid in the opposite direction.

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19
Q

What are the three factors that affect membrane fluidity?

A

Temperature, cholesterol, fatty acids

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20
Q

How does temperature affect membrane fluidity?

A

High temperature causes increased membrane fluidity. Low temperature causes decreased membrane fluidity.

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21
Q

Why does cholesterol decrease membrane fluidity at high temperatures?

A

At high temperatures, the phospholipids are spaced far apart. Cholesterol inserts itself between the phospholipid, making it harder for them to move.

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22
Q

Why does cholesterol increase membrane fluidity at low temperatures?

A

At low temperatures, phospholipids are tightly packed together. Cholesterol inserts itself between the tightly packed phospholipids thus creating a larger space for them to move and increasing membrane fluidity.

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23
Q

How do fatty acids affect membrane fluidity?

A

Saturated fatty acids decrease membrane fluidity because there are no double bonds, causing phospholipids to be packed tightly.
Unsaturated fatty acids have double bonds which create kinks, increasing the space between phospholipids and increasing membrane fluidity.

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24
Q

_______ proteins are located in the lipid bilayer.

A

Integral

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25
What are the two types of integral proteins?
Transmembrane proteins that pass completely through the lipid bilayer. Embedded proteins that only pass through one leaflet of the lipid bilayer and protrude either intracellularly or extracellularly.
26
________ proteins don’t touch the lipid bilayer, they are located on the intracellular side or extracellular side.
Peripheral
27
How are peripheral proteins bound to the lipid bilayer?
They are bound through noncovalent interactions to G proteins, polar head groups, other integral proteins, and in lipid raft regions.
28
What are lipid-anchored proteins?
They are proteins covalently anchored on the plasma membrane to hydrocarbon fatty acids in the lipid bilayer.
29
Where are carbohydrates located in the cell membrane and what role do they play?
Carbohydrate sugars are attached to proteins on the extracellular surface of the cell, forming a glycoprotein coat when interacting with water. They play an important role in cell signaling, “giving face to the cell”.
30
Where are gap junctions most prevalent in the body?
They are prevalent in the heart where they allow the rapid spread of ion current through cardiac muscle and between smooth muscle cells.
31
What are gap junctions made of?
They are channel proteins made of six connexin protein subunits arranged in a ring formation with a central opening. They pass through the lipid bilayers of cells connecting 2 cells together.
32
What is the function of gap junctions?
They allow for the passage of ions, amino acids, cAMP, ATP, and nucleosides between cells. These channels are regulated by phosphorylation.
33
Where are tight junctions found?
They are found in epithelial cells in the stomach, intestine, bladder, and capillaries in the blood brain barrier.
34
What is the function of tight junctions?
They are integral proteins that form continuous bands around the cell to prevent solute from leaking into the extracellular space between cells. They create a water-tight seal.
35
Where are desmosomes primarily found?
They are found in epithelial skin cells (epidermis), heart muscle, and the intestines.
36
What is the main function of desmosomes?
They aid in structural support and tensile strength of tissue. They connect cells together by binding to intermediate filaments in the cytoplasm and connecting cells via cadherin bridges in the ECM.
37
What is the main function of hemidesmosomes?
They are integrin protein sites involved in attaching cells to the ECM. Usually, hemidesmosomes connect to the basement membrane of the epithelium.
38
What are hemidesmosomes made of?
They are made of a dense plaque like proteins with projecting keratin filaments on the intracellular side, with a membrane spanning integrin protein that connects to laminin in the ECM.
39
Mutations in desmosomes and hemidesmosomes can cause ____________?
Fluid to leak below the epidermis causing severe skin blistering.
40
What is the primary thermodynamic motivator of passive transport in the cell?
Increase in entropy
41
Describe the process of osmosis.
It is passive transport of water molecules across a cell membrane that is impermeable to other solutes. This causes water to travel from an area of low solute concentration to high solute concentration.
42
What does it mean to say that osmotic pressure is a colligative property?
It means that osmotic pressure is dependent on the number of molecules, not the actual identity of the molecules. In other words, it is dependent on the molarity.
43
What kinds of molecules travel by simple diffusion across the cell membrane?
Small and nonpolar molecules, such as O2 and CO2. Some large molecules that have to be non-polar such as benzene rings. A special molecule, H2O, even though it is polar, it can still diffuse across the membrane given it’s very small size.
44
What is primary active transport?
It is a process that directly uses ATP to control the flow of molecules against their concentration gradient.
45
Give an example of primary active transport.
The sodium potassium pump, only present in animal cells, is a protein pump, which utilizes ATP to transport 3 Na ions outside the cell and 2 K ions inside the cell. Process: 1. 3 Na ions bind to the inside of the protein. 2. ATP is hydrolyzed to ADP releasing a phosphate group, which goes on to phosphorylate the pump. 3. Phosphorylation causes the protein pump to change shape and release the Na ions. 4. Then, 2 K ions bind to inside of the pump. 5. Phosphate group unbinds from the pump and causes it to change shape again. 6. K ions unbind and are released inside of the cell.
46
The sodium potassium pump has a higher affinity for sodium on the ________ side.
intracellular
47
The sodium potassium pump has a higher affinity for potassium on the __________ side.
Extracellular
48
True or False Carrier proteins only participate in active transport.
False. Carrier proteins can participate in both active and passive transport. In passive transport, binding of the ligand is sufficient enough for the carrier protein to change shape, allowing for molecules to flow down their concentration gradient.
49
What is secondary active transport?
It is active transport, that indirectly uses ATP to fuel a molecule flowing against its concentration gradient. Uses the energy from a molecule flowing towards its concentration gradient to fuel another molecule going against its gradient.
50
The two types of secondary active transport.
Symport which moves molecules in the same direction. Antiport which moves molecules in opposite directions.
51
What is endocytosis?
The process of the plasma membrane invaginating and engulfing material from the outside to bring inside the cell. There are more specific types.
52
What is exocytosis?
The process of secretory vesicles fusing with the plasma membrane to release intracellular material to the extracellular side.
53
What is pinocytosis?
Meaning “cell drinking”, it is the process of taking in extracellular fluid including water molecules necessary for the cell. Vesicles formed are small.
54
What is phagocytosis?
The process by which the cell takes in large particles such as viruses to eventually break them down inside the cell. 1. Cell comes in contact with the large particle/virus and the receptors on the virus/particle bind to specific surface receptors on the cell. (Indirect binding) 2. The cell membrane engulfs the large particle by extending its cytoplasm (pseudopods) and once the particle is inside the cell, it’s contained in a vesicle called a phagosome. 3. When the phagosome fuses with a lysosome, it becomes an endosome and starts to breakdown the material inside by actively lowering the pH of the vesicle.
55
What kinds of immune cells perform phagocytosis?
Neutrophils, macrophages, dendritic cells, and B lymphocytes
56
What is receptor mediated endocytosis?
The most specific type of endocytosis by which bulk amounts of specific molecules such as sugars or hormones can be taken into the cell by binding directly to specific cell surface receptors. Once molecules are bound, this triggers the plasma membrane to recruit clathrin proteins and the membrane to invaginate. The vesicle that forms inside is coated with clathrin.
57
True or false: Pinocytosis and receptor mediated endocytosis involve the cell membrane invaginating inward to form a vesicle, while phagocytosis involves the cytoplasm protruding outward through a pseudopod formation.
True
58
What establishes the ion concentration gradient?
It is established by active transporters, specifically the Na/K pump which ensures there is a lot of potassium inside the cell and a lot of sodium outside of the cell.
59
What contributes to the resting membrane potential?
Potassium leak channels directly contribute to the negative resting membrane potential by allowing K to leak out of the cell down its concentration gradient. Since K is positively charged, inside of the cell becomes negatively charged because of the Cl- ions that stay behind. Indirectly the concentration gradient fueled by active transporters drives the potassium out of the cell.
60
What are the general functions of lipids?
-Major component of the plasma membrane -Serve as co-enzymes in the electron transport chain -Serve as hormones -Serve as intracellular messengers that respond to extra cellular signals -Absorb light -Store energy
61
Are lipids amphipathic in nature?
Yes, they contain both hydrophilic and hydrophobic regions.
62
Phospholipid structure and function
Phospholipids make up the majority of the cell membrane. They are composed of a phosphate group and an alcohol which comprise the polar head and hydrophobic fatty acid tail. An R group can attach to the phosphate.
63
Name examples of phospholipids:
Phosphoethanolamine, phosphatidylserine (-), phosphoinositol (-)
64
What is the structure and function of fatty acids?
Fatty acids are made of long hydrocarbon chains with a carboxylic acid group at the end. Their main function is to make up the cell membrane and contribute to the membrane fluidity.
65
What are the two types of fatty acids?
Saturated fatty acids are those that don’t have double bonds in them. Unsaturated fatty acids contain double bonds, which create kinks.
66
What is the structure and function of glycerophospholipids?
They are a specific type a phospholipid which contains a glycerol molecule as its backbone. The glycerol is bonded by two ester linkages to two fatty acids. The glycerol is bonded to a phosphate group, which is then bonded to an additional polar head group. The polar head groups vary.
67
What is the structure of sphingolipids?
Sphingolipids have a sphingosine backbone which is made of a long hydrocarbon chain with a double bond connecting to 2 alcohol groups and an amine group. A fatty acid chain connects to the amine group and a polar head group connects to the outermost OH group.
68
What is the structure of a ceramide?
Has a sphingosine backbone with a fatty acid connected to the amine group and only a H atom as the polar head group. (It is the simplest type of sphingolipid)
69
What is the structure and function of sphingomyelins?
A class of sphingolipids that have contain phosphodiester bonds (phosphoethanolamine or phosphocholine) as their head group. They make up cells which produce myelin such as oligodendrocytes in the CNS and Schwann cells in the PNS.
70
What is the structure of glycolipids?
Glycolipids are a type of sphingolipid which have sugars that make up their head group. No phosphodiester bonds. There are 3 kinds of glycolipids: Cerebrosides - have only 1 sugar as the head group Globosides - have multiple sugars as the head group Gangliosides - have an oligosaccharide chain w/ sialic acid at the terminus that gives a negative charge to the head group
71
What is the structure and function of waxes?
They are composed of a long chain hydrophobic fatty acid esterified to long hydrocarbon chain alcohols. They are used as protection in plants against evaporation and parasites. Also provide membrane stability/structural integrity.
72
What is an isoprene unit?
C5H8 makes up one isoprene unit. Isoprene units make up terpenes.
73
What are terpenes?
They are a class of lipids built from isoprene units. They are produced by plants and have pungent smells and make up a lot of essential oils. Most importantly, they are metabolic precursors to steroids.
74
How are terpenes grouped?
They are grouped by the number of isoprene units that they are composed of.
75
How many isoprene units are in a monoterpene?
Two isoprene units making C10H16.
76
How many units make up sesquiterpene? Diterpene?
Three isoprene units. Four isoprene units.
77
How many isoprene units make up triterpene?
6 isoprene units.
78
How many isoprene units make up tetraterpene?
8 isoprene units.
79
What are terpenoids/isoprenoids?
They are derivatives of terpenes that have undergone oxygenation or rearrangement of their carbon skeleton meaning they have additional functional groups present.
80
What is the structure of steroids?
Made of terpenes; have a nonpolar structure of 3 cyclohexanes and 1 cyclopentane fused together.
81
What is the structure of cholesterol?
Cholesterol is a steroid, it is amphipathic meaning that it contains both hydrophilic and hydrophobic components. 3 cyclohexanes and 1 cyclopentane connected to a HC chain (tail). OH group connected to the ending cyclohexane ring.
82
What is the structure and function of prostaglandins?
They are lipid molecules, composed of an unsaturated fatty acid with 1 five carbon ring at the end. They act as paracrine or autocrine signaling molecules. They are present in many tissues and regulate the synthesis of cAMP —> cAMP regulates the action of many hormones
83
What is the structure of triglycerol/triglycerides?
Hydrophobic compound, composed of 3 fatty acids esterified to a glycerol backbone. The fatty acids can be unsaturated/saturated.
84
What is the function of triglycerides?
They are stored in cells as deposits in adipocytes for additional energy necessary to survive when other energy has been depleted in the body.
85
Where are tricylglycerols found in the body?
They are found in adipocytes underneath the skin, around mammary glands, and in the abdominal cavity.
86
What are the 4 fat soluble vitamins?
Vitamin A, Vitamin D, Vitamin E, and Vitamin K
87
What is the structure and function of vitamin A?
Also known as “carotene”. It is composed of an unsaturated hydrocarbon chain, and its functions include vision, growth, development, and immune function. A metabolite of vitamin A is retinal which is part of the photoreceptor transduction pathway in the human eye.
88
What is the structure and function of vitamin D?
Also known as “cholecalciferol”. It is part vitamin/part hormone. It had several rings as well as side chains. Vitamin D is converted to its active form in the liver and kidneys. Its function is to increase calcium and phosphate uptake in the intestines. it is important for the growth and development of bones and teeth.
89
What is the structure and function of vitamin E?
Also known as tocopherol and tocotrienol. it is composed of a hydrophobic substituted, aromatic ring, with a long isoprenoid side chain. It functions as a biological antioxidant that reacts with free radicals to prevent oxidative damage in the body.
90
What is the structure and function of vitamin K?
There are different groups of vitamin K called “phylloquinone and menaquinone” . They are composed of a long hydrocarbon chain with 2 cyclohexanes at the end. They are vital in posttranslational modifications to form prothrombin, which is a clotting factor in the blood.
91
What is saponification?
It is the process used to create soaps from triglycerides. Triglycerides are hydrolyzed using a strong base, such as sodium or potassium hydroxide. The products formed are the glycerol backbone and soap. Soap is important in increasing solvation helping oil and water combine to form micelles.
92
Which lipids are amphipathic?
Phospholipids, fatty acids, sphingolipids, and glycolipids
93
How do you determine the number of isoprene units in a complex molecule?
Count the number of carbons in the molecule and divide that number by five, to get your number of isoprene units.
94
Which lipids are not hydrolyzable?
Steroids, prostaglandins, fat-soluble vitamins
95
Which lipids are hydrolyzable?
Those which have ester linkages which can be cleaved by lipases. 1. Triacylglycerol 2. Sphingolipids 3. Waxes 4. Phospholipids

Malika Biochem MCAT (11 decks)

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