UNIT 5 BIOLOGY EXAM

Describe the parts of the phospholipid bilayer

• HYDROPHILIC phosphate head which is POLAR

• HYDROPHOBIC fatty acid tails which is NON-POLAR

What does it mean by the terms “polar” and “non-polar”?, give examples of the parts of the phospholipid bilayer that are polar and non-polar.

• Polar = attracted to water, such as the hydrophilic phosphate heads

• Non-polar = repelled by water, such as the hydrophobic fatty acid tails

State the two main features of the fluid mosaic model

• Fluid Part- Phospholipids and proteins can move laterally (side to side)

• Mosaic Part- Refers to how the phospholipid bilayer is embedded with different proteins

State the three roles of cholesterol in cell surface membranes

• Cholesterol adds mechanical stability

• Cholesterol increases rigidity

• Cholesterol prevents the loss of ions

Describe what a glycoprotein is and state the two main roles of glycoproteins in cell surface membranes

• Glycoproteins are carbohydrates covalently bonded to proteins,

• Function 1 - they act as receptors for hormones

• Function 2 - acts as antigens which allows cells to recognise each other as “self”

Describe what a glycolipid is and state the two main roles of glycolipids in cell surface membranes

• Glycolipids are carbohydrates covalently bonded to a phospholipid

• Function 1 - act as receptors for hormones

• Function 2 - acts as antigens which allows cells to recognise each other as “self”

Describe what a channel protein is and explain its role in the phospholipid bilayer

• Intrinsic (go across the whole bilayer) proteins that have a channel lined with hydrophilic amino acids

• They allow the transport of ions and polar molecules DOWN their concentration gradient.

Describe what a carrier protein is and explain its role in the phospholipid bilayer

• Intrinsic proteins that have a pocket lined with hydrophilic amino acids.

• They allow the transport of ions and polar molecules DOWN and AGAINST their concentration gradient, by changing shape

Describe what extrinsic proteins are and state the two main roles of extrinsic proteins in cell surface membranes

• Unlike intrinsic proteins, extrinsic proteins are only found on one side of the cell membrane

• Their functions include: Membrane bound enzymes & acting as antigens

Give one similarity and one difference between a channel protein and a carrier protein

Carrier Proteins:

• Changes shape & moves substances against their conc gradient

Both:

• Transport ions

• Go through the whole phospholipid bilayer

What is a Red blood cell, Phagocyte & Squamous endothelium of blood capillary

• Red blood cell - Main cellular component of blood and moves around at extremely high speeds & pressures

• Phagocyte - A type of white blood cell that regularly changes shape and can fit through small pores in capillaries

• SE - Makes up blood vessels called capillaries & are continuous hit by red blood cells which move at high speeds

1. Why do phagocytes have a low percentage cholesterol?

2. Why do red blood cells need more cholesterol than phagocytes?

3. Why do SE have a very high amount of cholesterol in their membrane?

1. They have to be flexible to move through small pores & capillaries, and carry out phagocytosis

2. They move at high speeds and pressure through the circulatory system, so need rigidity to keep their biconcave shape

3. They are continuously hit by RBC that move at high speed and pressure so need a lot of mechanical stability to prevent damage.

1. What is simple diffusion?

2. Both simple and facilitated diffusion is a passive process, what does this mean?

1. Net movement of small non polar particles from an area of a high conc to low conc, down their conc gradient. This is a passive process where these substances move between phospholipids.

2. Diffusion does not require any metabolic energy

1. What is facilitated diffusion?

2. What is a polar molecule?

1. Net movement of polar particles from a high to low conc, down their conc gradient. This is a passive process where these substances move between channel or carrier proteins.

2. Covalent molecules with an unequal distribution of electrons.

Describe one difference between facilitated diffusion and simple diffusion

• Both are passive processes (doesn’t require additional energy)

• Both move substances down their conc gradient, from a high to low conc

• FD moves polar substances + ions through intrinsic protein, whereas SD moves small non polar, lipid soluble substances between phospholipids.

Explain why small, uncharged, lipid soluble molecules can go through without the use of a protein

• They are non-polar and so are hydrophobic

• Therefore, they will not be repelled by the hydrophobic fatty acid centre of the bilayer

Describe what is meant by the phrase ‘lipid soluble’ and explain why the lipid soluble molecules can go through without the use of a protein

• It means dissolves in lipids

• Therefore, lipid soluble molecules are non-polar and so are hydrophobic and will not be repelled by the hydrophobic fatty acid tail

1. Give an example of a lipid soluble molecule

2. Name two intrinsic proteins involved in facilitated diffusion

1. Oxygen and steroid hormones

2. Channel and carrier proteins

Channel proteins transport molecules such as ions ( e.g. Na+). Channel proteins work in a specific way, explain what this means

It only changes shape for one chemical/ion

Explain how carrier proteins work

• Carrier proteins are specific, so they have a binding site for only on type of ion lined with hydrophilic amino acids.

• When the ion binds, the carrier protein changes shape, and transports the ions to the other side

State the chemical formula of glucose and suggest why it is unable to fit through gaps between phospholipids in the phospholipid bilayer- (simple diffusion)

Glucose = C6 H12 O6 (24 atoms)

• It is unable to fit through gaps between phospholipids in the phospholipid bilayer because it is too large and it is polar