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BIOL 204 > The Important of Membranes > Flashcards

The Important of Membranes Flashcards

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1
Q

What is the fluid mosaic model?

A

It suggests that membranes are dynamic structures with proteins moving within a fluid made up of lipid molecules.

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2
Q

What is the lipid bilayer?

A

A double layer of lipid molecules in biological membranes, less than 10 nm thick, where lipids move sideways but rarely flip layers

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3
Q

Why is the fluid nature of the lipid bilayer important?

A

It is crucial for membrane function.

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4
Q

What roles do membrane proteins play?

A

They are involved in transport, attachment, signal transduction, and some anchor the cytoskeleton filaments.

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5
Q

What are glycoproteins and glycolipids?

A

Lipid and protein molecules in the membrane with carbohydrate groups attached.

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6
Q

How does the composition of lipids and proteins vary in different membranes?

A

For example, the inner mitochondrial membrane has 76% protein and 24% lipid, while the plasma membrane has roughly equal amounts, and myelin has 18% protein and 82% lipids

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7
Q

What is the role of proteins on the internal side of the plasma membrane?

A

They bind to components of the cytoskeleton.

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8
Q

How do hormones and growth factors interact with the plasma membrane?

A

They bind to receptor proteins on the external surface.

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9
Q

What did the 1970 study by David Frye and Michael A. Edidin demonstrate?

A

The fluid nature of membranes, showing that membrane proteins can move and intermingle.

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10
Q

What did the freeze-fracture technique reveal about membranes?

A

It showed membrane asymmetry, with differences in size, number, and shape of embedded proteins between the two sides

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11
Q

What are phospholipids?

A

Amphipathic molecules with hydrophilic heads and hydrophobic tails, forming the lipid bilayer of membranes.

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12
Q

How does the fatty acid composition affect membrane fluidity?

A

Saturated fatty acids make the membrane less fluid, while unsaturated fatty acids increase fluidity.

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13
Q

How do organisms maintain optimal membrane fluidity?

A

By adjusting the proportion of unsaturated fatty acids in response to temperature changes.

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14
Q

What role do sterols like cholesterol play in membrane fluidity?

A

At high temperatures, they reduce fluidity by restraining lipid movement; at low temperatures, they prevent tight packing of fatty acids, maintaining fluidity.

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15
Q

What are the two major types of membrane proteins?

A

Integral membrane proteins and peripheral membrane proteins

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16
Q

What is the primary role of membrane proteins?

A

Membrane proteins determine the membrane’s function and make each membrane unique.

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17
Q

What are the four key functions of membrane proteins?

A

Transport, enzymatic activity, signal transduction, and attachment/recognition.

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18
Q

How do transport proteins function in membranes?

A

They provide hydrophilic channels for specific molecules or change shape to shuttle molecules across the membrane.

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19
Q

What is the role of enzymatic membrane proteins?

A

Some enzymes are membrane proteins, such as those in the respiratory and photosynthetic electron transport chains.

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20
Q

What do receptor proteins do in signal transduction?

A

Receptor proteins bind specific chemicals like hormones, triggering internal changes that lead to signal transduction through the cell.

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21
Q

What is the function of attachment/recognition membrane proteins?

A

They serve as attachment points for cytoskeleton elements and components involved in cell-cell recognition.

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22
Q

What are integral membrane proteins?

A

Proteins embedded within the phospholipid bilayer, with some traversing the entire bilayer (transmembrane proteins).

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23
Q

What is the structure of transmembrane proteins?

A

They have nonpolar domains that interact with the lipid bilayer and polar domains exposed to the aqueous environments.

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24
Q

How can the primary structure of a transmembrane protein indicate its nature?

A

It shows stretches of nonpolar amino acids about 17 to 20 amino acids in length, corresponding to the length needed to span the lipid bilayer.

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25
What are peripheral membrane proteins?
Proteins located on the membrane's surface that do not interact with the hydrophobic core, held by noncovalent bonds.
26
What role do peripheral proteins on the cytoplasmic side often play?
They often form part of the cytoskeleton and include key enzymes involved in respiratory and photosynthetic electron transport.
27
What kind of amino acids do peripheral proteins have?
They have a mix of polar and nonpolar amino acids.
28
What is passive transport?
The movement of substances across a membrane without the use of chemical energy (e.g., ATP), driven by diffusion.
29
What is diffusion?
The net movement of molecules from an area of higher concentration to an area of lower concentration, driven by an increase in entropy.
30
What factors influence the rate of diffusion?
The concentration gradient; a larger gradient results in a faster rate of diffusion.
31
What is simple diffusion?
Movement directly across a membrane without a transporter, used by small nonpolar molecules, steroid hormones, and small uncharged molecules.
32
What is facilitated diffusion?
Movement across a membrane through specific transport proteins, used by polar and charged molecules.
33
What are channel proteins?
Transmembrane proteins that form hydrophilic pathways for molecules to cross the membrane, including specific channels for ions and water.
34
What are gated channels?
Channel proteins that switch between open and closed states to control ion movement, such as voltage-gated ion channels for nerve conduction.
35
What are carrier proteins?
Transmembrane proteins that bind specific solutes and undergo conformational changes to transport them across the membrane.
36
How can you determine if a molecule is transported by facilitated diffusion?
The rate of movement is faster than predicted by chemical structure alone and can reach saturation when all transporters are occupied.
37
What is osmosis?
The passive diffusion of water across a membrane, moving from regions of lower solute concentration to regions of higher solute concentration.
38
What happens to cells in hypotonic solutions?
Water enters the cell, potentially causing animal cells to burst, while plant cells resist bursting due to turgor pressure.
39
What happens to cells in hypertonic solutions?
Water leaves the cell, causing it to shrink.
40
What are isotonic solutions?
Solutions where water concentration is balanced inside and outside the cell, preventing osmotic imbalance and cell bursting.
41
What distinguishes active transport from passive transport?
Active transport moves molecules against their concentration gradient using energy, while passive transport relies on diffusion and moves substances down a concentration gradient.
42
What energy source is commonly used in active transport?
ATP (adenosine triphosphate)
43
What are the main functions of active transport?
Uptake of essential nutrients, removal of waste, and maintenance of ion concentrations.
44
What is primary active transport?
Transport where the same protein that transports the molecules also hydrolyzes ATP to power the transport.
45
What is secondary active transport?
Transport that uses the concentration gradient of ions built up by primary active transport to indirectly drive the transport of different molecules.
46
What are proton pumps (H⁺ pumps)?
Primary active transport pumps that move H⁺ ions from the cytoplasm to the cell exterior, generating membrane potential and maintaining low pH in organelles like lysosomes and vacuoles
47
What are calcium pumps (Ca²⁺ pumps)?
Primary active transport pumps that push Ca²⁺ ions from the cytoplasm to the cell exterior and into ER vesicles, maintaining low cytoplasmic Ca²⁺ levels.
48
What is the function of sodium-potassium pumps (Na⁺/K⁺ pumps)?
These pumps move three Na⁺ ions out and two K⁺ ions into the cell per cycle, creating an electrochemical gradient crucial for nerve impulse transmission and muscle contraction.
49
What are the two mechanisms of secondary active transport?
Symport (cotransport) and antiport (exchange diffusion).
50
What is symport (cotransport)?
A mechanism where the solute and the driving ion move in the same direction through the membrane.
51
What is antiport (exchange diffusion)?
A mechanism where the solute and the driving ion move in opposite directions through the membrane.
52
What is an example of symport in secondary active transport?
The cotransport of glucose and amino acids with Na⁺ ions.
53
What is an example of antiport in secondary active transport?
The exchange of Cl⁻ and bicarbonate ions in red blood cells.
54
How does secondary active transport utilize ion gradients?
It uses the ion gradients established by primary pumps as an energy source to move other molecules.
55
What are endocytosis and exocytosis?
Specialized mechanisms for transporting large molecules that cannot pass through the plasma membrane via passive or active transport, involving vesicles and requiring energy.
56
What is exocytosis?
The process by which cells expel materials to the exterior through secretory vesicles that fuse with the plasma membrane, releasing their contents outside the cell.
57
Give examples of exocytosis.
Glandular cells secreting peptide hormones or milk proteins, digestive tract cells secreting mucus and enzymes, and plant cells secreting carbohydrates to build cell walls.
58
What is endocytosis?
The process by which cells internalize substances from their exterior environment through vesicle formation by inward folding of the plasma membrane.
59
What is bulk-phase endocytosis (pinocytosis)?
The non-specific uptake of extracellular fluid and dissolved substances without the need for specific receptors.
60
What is receptor-mediated endocytosis?
A selective process where specific molecules bind to receptors on the cell surface, leading to the formation of endocytic vesicles reinforced by clathrin.
61
What happens to vesicles after receptor-mediated endocytosis?
They lose their clathrin coats inside the cell, fuse with lysosomes, and the contents are digested into useful molecules like amino acids and monosaccharides.
62
What is phagocytosis?
A specialized form of receptor-mediated endocytosis where cells engulf large particles, cell debris, or other cells by extending cytoplasmic lobes to form a large endocytic vesicles
63
What roles do exocytosis and endocytosis play?
Secretion of materials, nutrient uptake, and membrane recycling, maintaining a balance in plasma membrane surface area and proper membrane function.
64
Why are exocytosis and endocytosis essential?
They dynamically regulate the cell’s interaction with its environment, crucial for nutrient uptake, waste removal, and the secretion of substances necessary for cellular communication and structural integrity.
65
What is the role of cellular membranes in signal perception and transduction?
Cellular membranes help detect signals from other cells or external factors and transduce them into cellular responses necessary for maintaining homeostasis.
66
What are the three main steps of signal transduction?
Reception, transduction, and response
67
What happens during the reception step of signal transduction?
Signal molecules (ligands) bind to specific receptors on target cells.
68
Where can receptors be located in cells?
On the plasma membrane, within internal membranes like the ER, or as soluble cytoplasmic proteins.
69
What occurs during the transduction step?
Signal reception triggers a series of intracellular changes known as a signaling cascade.
70
What is the response step in signal transduction?
The transduced signal leads to a specific cellular response, such as changes in enzyme activity or gene expression.
71
What are membrane receptors?
Integral proteins that extend through the cell membrane with a specific binding site for signal molecules.
72
How do membrane receptors function?
The binding of the signal molecule alters the receptor's structure, transmitting the signal through the membrane and activating the receptor's cytoplasmic end.
73
What are protein kinases?
Enzymes that transfer phosphate groups from ATP to proteins, initiating a phosphorylation cascade.
74
What are phosphorylation cascades?
Chains of phosphorylation reactions where one kinase activates another, leading to the final target protein which brings about the cellular response.
75
What are protein phosphatases?
Enzymes that remove phosphate groups, turning off the signal transduction pathway when the signal is no longer present.
76
What is signal amplification in signal transduction pathways?
The process where the signal is amplified at each step, allowing a small number of signal molecules to produce a significant cellular response.
77
Give an example of a signal transduction pathway.
1. Reception: A signal molecule binds to a receptor on the plasma membrane. 2. Transduction: The activated receptor initiates a phosphorylation cascade. 3. Response: The final protein in the cascade triggers a cellular response, such as activating a transcription factor that alters gene expression.
78
Why are membranes and their associated proteins fundamental in cell signaling?
They convert extracellular signals into specific intracellular actions, ensuring that cells and organisms can adapt to their changing environments, essential for maintaining cellular function and overall organismal homeostasis.

BIOL 204 (6 decks)

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