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Fundamentals of Life Science > Biological membranes > Flashcards

Biological membranes Flashcards

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Biology 101 flashcards
1
Q

What is the fluid mosaic model?

A

Membranes behave like fluids

A mosaic of different things

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2
Q

What do eukaryotic cell membranes contain?

A

Phospholipids
Cholesterol
Glycolipids

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3
Q

What does amphipathic mean?

A

Both hydrophobic and hydrophilic

Phospholipids are amphipathic

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4
Q

What is a phospholipid made of?

A

A hydrophilic head

A hydrophobic tail

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5
Q

What makes the tail of the phospholipid molecule?

A

Two fatty acid chains

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6
Q

Are fatty acids saturated or unsaturated?

A

Either

Unsaturated fatty acids have a kink in their chain

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7
Q

What is the head of the phospholipid made of?

A

In most cases, glycerol, phosphate and and another compound

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8
Q

Name the four major phospholipids

A

Phosphatidyl-ethanolamine
Phosphatidyl-serine
Phosphatidyl-choline
Sphingomyelin

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9
Q

What are the two categories of phospholipid?

A

Phosphoglycerides

Sphingolipid

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10
Q

What is a lipid micelle?

A

A spherical molecule of only one layer of phospholipids

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11
Q

Why do lipid bilayers spontaneously close to form sealed compartments?

A

It is energetically favourable

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12
Q

Why is the fluidity of a membrane important?

A

Allows diffusion and interaction
Fusion with other membranes
Formation of daughter cells
Cell motility

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13
Q

How does a membrane stay fluid at lower temperatures?

A

A higher number of unsaturated fatty acid chains

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14
Q

What is the role of cholesterol in the lipid bilayer?

A

Cholesterol intercalates between membrane phospholipids

This decreases the membrane permeability to small molecules

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15
Q

Where are lipid bilayers formed?

A

In the endoplasmic reticulum

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16
Q

How is the phospholipid molecule made?

A

Fatty acids are made in the cytosol and transported to the endoplasmic reticulum by binding proteins
They are embedded in the membrane
Phosphate and choline are added

17
Q

Where in the endoplasmic reticulum does phospholipid synthesis occur?

A

The outer cystolic leaflet

18
Q

What is scramblase?

A

Catalyses transbilayer movement so the phospholipids are distributed equally between inner and outer leaflets

19
Q

Where does the inner luminal leaflet of the ER end up?

A

As the external leaflet of the cell membrane

20
Q

What is flippase?

A

Flips PE and PS from extracellular leaflet to the cytosolic leaflet

21
Q

What are glycolipids?

A

Found on the extracellular leaflet
Based on sphingosine
Contain sugar

22
Q

Where does glycosylation occur?

A

In the lumen of the ER

23
Q

Name the two categories of membrane protein

A

Integral

Peripheral

24
Q

How are integral membrane proteins inserted into the membrane?

A

Synthesised by ribosomes in the cytoplasm
Contain hydrophobic signal peptide (15-20 aa) at their N-terminal end
This directs polypeptide into translocator on ER membrane
Translocated through membrane and cleaved into ER lumen
Signal peptide cleaved

25
Q

How are peripheral proteins inserted into the membrane?

A

Contain hydrophobic signal at N-terminal
Translocated through membrane until a stop transfer signal is reached
Translocator discharges protein laterally into bilayer
Signal peptide cleaved

26
Q

How are double pass peripheral proteins inserted into the membrane?

A

The signal peptide is internal, not found at the N-terminus

Signal peptide not cleaved

27
Q

What is the function of glycoproteins?

A

Cell recognition
Inflammatory response
Protection

28
Q

What is the glycocalyx?

A

Carbohydrate rich layer surrounding cells
Composed of glycoproteins and glycolipids
Protects cells against mechanical and chemical damage

29
Q

What is the largest protein complex in a cell

A

The nuclear pore complex

30
Q

Describe the nuclear pore complex

A

400 individual proteins
30 distinct proteins (nucleoporins)
Both integral and peripheral membrane proteins

Fundamentals of Life Science (24 decks)

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