Cell Membranes, Transport Of Small And Large Molecules Lectures 2.1-2.3 Flashcards

1
Q

What are cell membranes?

A

-selectively permeable barriers
-maintain constant internal environment and enclose cell contents
-very thin

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2
Q

Phospholipid molecule:

A

-has a dynamic structure so components are free to move around
*amphipillic: both hydrophilic and hydrophobic parts
*polar head: negatively charged phosphate group
*non polar tail: no charge
*phospholipid: “self-assembles” to create the bilayer. They migrate but rarely flip

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3
Q

What are the two different types of tails?

A

Saturated and Unsaturated
Saturated: single bonds only
Unsaturated: at least one double bond
Double bond creates a kink in the fatty acid chain of the tail

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4
Q

What do higher concentrations of saturated fatty acids cause?

A

Reduces cell membrane fluidity

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5
Q

What do higher concentrations of unsaturated acids cause?

A

They promote membrane fluidity

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6
Q

What does concentrations of unsaturated phospholipids affect?

A

It affects membrane fluidity

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7
Q

What are the two types of carbohydrates?

A

*glycolipids
*glycoproteins

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8
Q

Three major roles of carbohydrates

A

-maintain membrane stability and cell protection and aids in cell adhesion and recognition.

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9
Q

Tell me about cholesterol:

A

-is a lipid (approx 20% of the membrane lipid is cholesterol)
-has polar and non polar regions
-wedges itself between the phospholipid tails
-is able to migrate and flip between the membrane layers

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10
Q

Proteins:

A

-proteins are able to serve different functions such as:
Enzymes, carrier proteins, channel proteins, receptors, cell adhesion and recognition.

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11
Q

Two main types of proteins?

A

Integral and peripheral

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12
Q

Integral proteins:

A

-firmly inserted into the membrane
-span the bilayer of the membrane
-transmembrane protein is hydrophobic
-extracellular and cytosolic portions are hydrophilic
-carrier proteins and channels are integral proteins

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13
Q

Peripheral proteins:

A

-loosely attached to the membrane
-can be removed from the membrane with minimal disruption

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14
Q

What is membrane fluidity affected by?

A

-extreme temperatures; either hot or cold
-concentration of unsaturated fatty acids
-cholesterol levels

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15
Q

Membrane fluidity: what does a low temperature cause?

A

Less kinetic energy, phospholipids pack together and membranes have less fluid

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16
Q

Membrane fluidity: what does a high temperature cause?

A

More kinetic energy, phospholipids move further away and membranes have more fluid

17
Q

Membrane fluidity: what does having cholesterol cause?

A

It maintains fluidity by preventing lipids from getting too close together or too far apart from each other.

18
Q

Red blood cells?

A

Equal amounts of lipid, protein and a small amount of carbohydrate

19
Q

Nerve cells?

A

Higher amounts of lipid in the cell membrane (80%)

20
Q

Passive transport?

A

-moves down a concentration gradient
Three types: simple diffusion, facilitated diffusion and osmosis
-uses inherent kinetic energy

21
Q

Active transport?

A

-moves against a concentration gradient
-has directionality
-requires a specific carrier protein
Two types: primary and secondary
-needs external energy source

22
Q

Simple diffusion?

A

-small, uncharged non polar molecules
Properties:
-no metabolic energy is required
-uses kinetic energy
-the rate of diffusion is proportional to the concentration gradient

23
Q

Facilitated diffusion?

A

-small polar molecules; H2O, glucose etc
-uses specific proteins
-the rate of diffusion is proportional to the concentration gradient

24
Q

Simple diffusion and facilitated diffusion kinetics:

A

Simple diffusion= linear relationship between concentration and rate of diffusion
Facilitated diffusion= the rate of diffusion reaches a plateau since the proteins become fully occupied

25
Q

What is osmosis?

A

-net movement of water down a concentration gradient
-water is highly polar however some small amounts can ‘sneak’ through the membrane
-water moves freely and reversibly via a specific protein channel; aquaporins
-bulk movement of water is facilitated diffusion

26
Q

Primary active transport:

A

-movement of Na+ and K+ uses the Na+/K+/ATPase pump
-maintains ion concentration differences inside the cell
-hydrolysis of ATP results in= phosphorylation of the pump —> results in conformational change of pump
-causes transport of 3Na+ out and 2K+ into the cell

27
Q

Secondary active transport (co-transport):

A

movement of two substances at the same time;
*A substance against its concentration gradient—> active transport
*Ion movement down its concentration gradient—> usually facilitated diffusion
-energy used for secondary active transport comes from the electrochemical gradient across the membrane.

28
Q

What are the two types of secondary active transports?

A

Symport;
*transported substances move in the same direction
*Na+/Glucose transporter
-Antiport;
*Transported substances move in the opposite direction
-Na+/Ca2+ exchanger- uses the Na electrochemical gradient to transport Ca2+ out of the cell.

29
Q

What is endocytosis?

A

Moves large molecules into the cell
Three types: phagocytosis, pinocytosis and receptor- mediated

30
Q

What is exocytosis? And what is it used for?

A

Moves large molecules out of the cell
*Used for: hormone secretion, neurotransmitter release and mucous secretion

31
Q

What are vesicles? And what are they made up of?

A

-vesicular transportation of large molecules
*bubble-like membranous sacs
*made up of phospholipid bilayer containing fluid
*transport bubble
*protects substances being transported

32
Q

Endocytosis- phagocytosis

A

ingestion of large particles by specialised cells (phagocytes -> immune system)
-macrophages
-certain white blood cells
*used for removing bacteria and debris
*when bacteria binds to a phagocyte the cell membrane wraps itself around the particle= results in a phagosome containing the particle

33
Q

Endocytosis- pinocytosis

A

-occurs in most cells
*process used to take in extracellular fluid with dissolved substances
*droplet enters the cell and fuses with an endosome (sorting vesicle)

34
Q

Endocytosis- receptor mediated

A

*main mechanism for specific uptake of macromolecules
*very selective method
*uptakes substances (hormones, cholesterol) found in small amounts
*receptors for this are specific membrane proteins

35
Q

Exocytosis

A

*substances are being moved out the cell—> hormones and waste products
*process is stimulated by a cell-surface signal that results in these steps:
• substance is enclosed in a vesicle
• Transported to plasma membrane
• Vesicle attaches to the ‘docking’ sites on the membrane
• Fuses with membrane and ejects substances