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SL12100 Health and Disease Y1 > Lecture 6 - cell membrane > Flashcards

Lecture 6 - cell membrane Flashcards

1
Q

What are carbohydrates generically comprised of? Why are they water soluble?

A

carbon, hydrogen and oxygen atoms. Linked to most carbon toms are hydrogen and hydroxyl groups. The presence of hydroxyl groups means they are water soluble.

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2
Q

What are monosaccharides?

A

they are the monomers of carbohydrates

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3
Q

What is the most abundant monosaccharide?

A

glucose

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4
Q

give the molecular formula for glucose

A

C6H12O6

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5
Q

Describe how many carbon atoms most monosaccharides have and the most common shapes

A

5-6 carbon atoms- pentoses and hexoses

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6
Q

Draw and describe the structure of glucose

A
  • Glucose has five carbon atoms and an oxygen atom which form a ring that lies in a flat plane. The hydrogen and hydroxyl groups of each carbon lie above and below the plane of the ring.
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7
Q

Galactose is also a common example of a monosaccharide. How does the structure of galactose differ to glucose?

A

If one of the hydroxyl groups below the ring in glucose is shifted to a position above the ring, a different monosaccharide is produced- galactose.

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8
Q

What is a disaccharide?

A

carbohydrates composed of two monosaccharides

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9
Q

Sucrose is an example of disaccharide. What two monomers is sucrose made up of?

A

glucose and fructose

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10
Q

Explain the reaction that forms sucrose

A

the two monosaccharides- glucose and fructose- react in a dehydration reaction. A hydroxyl group is removed from one monomer and the hydrogen from another, forming water and creating a covalent glycosidic bond between the monomers to form sucrose.

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11
Q

The reaction that forms sucrose is reversible. Explain.

A

if a water is added to the glycosidic bond in sucrose, the two monosaccharides will uncouple.

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12
Q

Give two other disaccharides and where they come from and the monomers that make them.

A

maltose (glucose glucose) formed during digestion of large carbs AND lactose (glucose galactose) found in milk.

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13
Q

What is a polysaccharide?

A

These are made up of many monosaccharide units/monomers joined together to form polymers

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14
Q

Example of polysaccharide in plant cells

A

starch

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15
Q

Example of polysaccharide in human cells.

A

glycogen

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16
Q

describe the structure of glycogen

A
  • Glycogen is made up of many glucose molecules joined by alpha 1,6 and alpha 1,4 glycosidic bonds- as a result, it is a branched polysaccharide.
  • The numbers of the bonds refer to which carbons are involved in the bond.
  • Glycogen can contain up to around 100,000 glucose monomers.
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17
Q

glucose is referred to as blood sugar. Why?

A

major monosaccharide found in blood.

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18
Q

Glycogen exists in the body as an energy store- a reservoir of energy. Where is the energy in glycogen actually stored?

A

between the chemical bonds within the individual glucose monomers

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19
Q

Where is glycogen found in the body?

A

liver

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20
Q

How does liver regulate the level of glucose in the blood?

A

Hydrolysis of glycogen occurs during periods of fasting. Glucose is released into the blood preventing blood glucose decreasing to dangerously low concentrations.

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21
Q

How are sugars used in the extracellular matrix?

A

The extracellular matrix is a network of proteins and other molecules- like sugars- which surround, support and give structure to cells and tissues in the body. This matrix helps attach cells to other cells (scaffold for cell attachment) and transmits information to cells growing, differentiating and migrating.

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22
Q

Cells use sugars in glycosylation to form…

A

glycoproteins and glycolipids.

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23
Q

What are lipids? - describe basic structure.

A

Lipids are molecules composed mainly of hydrogen and carbon bonds linked by non-polar covalent bonds. Therefore, lipids are nonpolar and are not soluble in water.

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24
Q

Roles of lipids

A

component of cell membranes, source of energy, important signalling molecules

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25
Q

Give four types of lipids

A
  • Steroids
  • Fatty acids
  • Triglycerides
  • Phospholipids
26
Q

Steroids have a different structure to other lipids. Describe.

A

a structure of 4 interconnected rings (of carbon atoms) which forms the skeleton. They may have functional groups attached to the chains- like hydroxyl groups which are polar, but not enough to make them water soluble.

27
Q

Different steroids arise due to…

A

functionalisation of rings and changing the side chains. Functional groups/side chains alter properties.

28
Q

give examples of steroids

A

cholesterol, testosterone, corticosteroids, bile acids.

29
Q

What are fatty acids? Draw one

A

chains of hydrogen and carbon atoms(alkyl chains) with a carboxyl group at the end.

30
Q

Common chain lengths

A

14,16,18 carbons.

31
Q

What are saturated fatty acids?

A

carbons in the alkyl chains are linked by single bonds

32
Q

Unsaturated fatty acids

A

carbons linked by double bonds

33
Q

Monounsaturated Vs. Polyunsaturated

A

one double bond, many double bonds.

34
Q

When do triglycerides form?

A
  • They form when one glycerol, a three-carbon alcohol, bonds to three fatty acids. Each of the three hydroxyl groups in a glycerol is bonded to the carboxyl group of a fatty acid by a dehydration reaction (3 water molecules are produced)
  • reaction is reversible. reversed by hydration/hydrolysis.
35
Q

How is there variation in triglycerides?

A
  • The three fatty acids are not usually identical; therefore, a variety of triglycerides can be formed with fatty acids of different chain lengths and degrees of saturation.
36
Q

Triglycerides are found where in the body? What is their role?

A

Present in the blood and can be synthesized in the liver. They are stored in great quantities in adipose tissue, where they serve as an energy reserve for the body, particularly when a person is fasting or requires additional energy (exercise).

37
Q

How are triglycerides broken down in adipose tissue? What happens to the fatty acids produced?

A
  • Hydrolysis releases the fatty acids from triglycerides in adipose tissue, the fatty acids enter the blood and are carried to tissues and organs where they can be metabolized to provide energy for cell functions.
38
Q

What are structure of phospholipids?

A
  • Similar overall structure to triglycerides but the third hydroxyl group of glycerol is attached to a phosphate rather than a fatty acid
  • A small polar/ionized nitrogen- containing molecule is attached to this phosphate.
  • This means that phospholipids have a polar region at one end and a non-polar region (fatty acid chains) at the other end.
  • Amphipathic
39
Q

Due to being amphipathic how do phospholipids arrange in water?

A

in aqueous solution they become organised in clusters with their polar ends attracted to water molecules and their non-polar fatty acid ends attracted to each other.
- These are called micelles- single lipid layers

40
Q

What is a liposome and what are they used for?

A

These are like micelles but have a bilayer rather than a single lipid layer. These are used in drug delivery.

41
Q

Describe the structure of a cell membrane.

A
  • Cell membrane is a lipid bilayer containing embedded proteins. The major membrane lipid= phospholipids.
  • As we know, the phospholipids are amphipathic- has a polar and non-polar end.
  • The phospholipids organise in such a way that the non polar fatty acid chains face towards the middle and the polar regions are orientated towards the surface of the membrane due to their attraction with water in the extracellular fluid and cytosol.
42
Q

The cell membrane is fluid. Why? Effects of this?

A

The cell membrane is fluid- lipids and entities dissolved within the layer can diffuse through it. This fluidity is because there are no chemical bonds linking the phospholipids to each other or to membrane proteins- there is a lateral movement from the molecules. Also, the fatty acid chains can bend and wiggle

43
Q

What do cholesterol do in the phospholipid bilayer?

A

effect fluidity of the membrane

44
Q

Function of the membrane/structures found within it.

A
  • Boundaries between cells and environment
  • Selective barrier to the passage of different molecules- selectively permeable. Some things get across easily and some with difficulty. If they can’t get across the proteins are needed to help them
  • Anchor cells to adjacent cells and to the extracellular matrix
  • Detect chemical signals from other cells
45
Q

What does selective permeability mean?

A

-Diffusion rates of molecules through the membrane depend on ionic charge and size.
-Non polar molecules have a high diffusion rate- this is because non polar molecules can dissolve in the non polar regions of the membrane.
- polar molecules diffuse slowly or not at all.
-small molecules have a high diffusion rate, large molecules have a low diffusion rate

46
Q

Give examples of molecules that diffuse straight through the membrane

A

CO2, O2, fatty acids, steroid hormones

47
Q

What is diffusion?

A
  • Diffusion is the net movement of molecules from an area of high to low concentration until equilibrium is reached. It is a movement influenced by electrochemical gradient (concentration and charge). It is a net movement- diffusion occurs in both directions.
48
Q

What is osmosis?

A
  • Osmosis – the net movement of water molecules across a partially permeable membrane down the concentration gradient until equilibrium is reached. Water transport across membranes.
49
Q

What are protein transporters/carriers?

A

Membrane proteins which can perform both passive and active transport of molecules.

50
Q

Name three protein transport/carrier mechanisms.

A

ion channels, transporters/carrier proteins, pumps/carriers

51
Q

Describe ion channels.

A

this is a type of facilitated diffusion (passive process). Some of the proteins which span across the membrane are ion channels which allow ions to diffuse across the membrane. These can show selectivity for the type of ions that diffuse through them. Eg. K+ channels only allow potassium to diffuse through them.

52
Q

Describe transporters.

A

this is another type of facilitated diffusion (passive process). Molecules which are too polar to diffuse through the bilayer and too big to diffuse through the ion channels (eg. Amino acids and proteins) will enter the cell by the help of transporters. These are proteins in the cell membrane, The molecule binds to specific site on transporter. The transporter protein undergoes change in shape and exposes the same binding site on the opposite side of the membrane. The molecule then dissociates from the binding site. It is now in the cell.

53
Q

Describe pumps

A

This is not a passive process, requires energy, active transport. A substance is moved uphill across the membrane, against the concentration gradient. The substance binds to a specific site on the carrier and it changes shape which results in the molecule being moved across the membrane

54
Q

Describe the sodium/potassium pump

A
  • The sodium/potassium pump is found in many cell membranes.
  • Powered by ATP, the pump moves sodium and potassium ions in opposite directions across the conc. gradient
55
Q

What is exocytosis?

A

membrane bound vesicles in the cytoplasm will fuse with plasma membrane and release contents out of the cell. A way of getting substances out of the cell.

56
Q

What is endocytosis?

A

regions of plasma membrane will fold into the cell forming pockets which pinch off to form intracellular membrane bound vesicles

57
Q

Name three types of endocytosis

A
  • pinocytosis
  • phagocytosis
  • receptor mediated
58
Q

Describe pinocytosis

A

an endocytosis vesicle encloses a small volume of extracellular fluid (made up of water and dissolved solutes like ions and nutrients)

59
Q

Describe phagocytosis

A

cell engulf bacteria/ large particles like cell debris from damaged tissue. Extensions of plasma membrane fold around the particles, engulfing it entirely. Large vesicles/phagosomes are formed and are internalised into the cell. The phagosomes fuse with lysosomes which release enzymes and destroy contents of the phagosomes.

60
Q

Describe receptor mediated endocytosis.

A

SPECIFIC. Certain molecules bind to specific proteins on outer surface of membrane (receptors). The plasma membrane folds and pinches off to form vesicles containing specific molecules.

SL12100 Health and Disease Y1 (18 decks)

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