Biol 1057 - The cell and the membrane

Question 1

Outline the ideas in the modern cell theory

Answer 1

• All cells have the same basic chemical composition
• All cells use energy
• All cells genetic material that is duplicated ia passed on as each cell
  divides

Question 2

Outline the differences between prokaryotic and eukaroytic cells

Answer 2

P
* No nucleus
* Circular DNA as a single chromosome
* No organelles, just ribosomes
* Most are 0.2 μm – 2.0 μm
* Unicellular only
E
* Membrane bound nucleus
* Linear DNA organized into multiple chromosomes
* Membrane bound organelles
* Most are 5 μm – 100 μm

Question 3

Outline the first type of cells

Answer 3

• The first group of cells in an embryo are all identical, unspecialized however become specialised after

Question 4

Quick recap of cell organelles

Question 5

Describe what is meant by the plasma membrane and define fluid mosaic model

Answer 5

• A selectively permeable barrier that separates the cell’s internal environment from its external surroundings
  FLUID: phospholipids are free to
  move within the layer
  MOSAIC: : there are number of
  proteins or other organic
  molecules embedded in the
  membrane

Question 6

Describe the main component of cell membranes

Answer 6

Phospholipids aligned as a bilayer allows for movement
=Hydrophillic heads attracted to water
=Hydrophobic tails repelled by water
➢Allow lipid-soluble substances in
and out of the cell
➢Prevent water-soluble substances
to enter and leave the cell

Question 7

Describe the 2 types of protein in the cell membrane & briefly outline function

Answer 7

PERIPHERAL PROTEIN
- Provide mechanical support
- OR Attached to proteins or lipids to form glycolipids & glycoproteins
- Involved in cell signalling, as receptors
INTEGRAL
- Either Channel or carrier protein
- Involved in the transport of molecules across the membrane

Question 8

Describe the role of cholestrol in the cell membrane

Answer 8

• Restrict lateral movement of other molecules in the membrane which improves tability
• Therefore membrane less fluid at high temperatures

Question 9

Describe what type of molecules can simply diffuse across the bilayer?

Answer 9

• Lipid soluble, Non-polar & Very small

Question 10

Outline the factors affecting membrane structure

Answer 10

• Temperature: high temperature so more kinetic energy so more movement. Membrane becomes more fluid,
  increased permeability. High temperatures denature proteins.
• Solvents: organic solvents (alcohols, alkenes) dissolve membranes. Non-polar alcohol enters membrane
  disrupting the structure.

Question 11

Outline the difference between passive and active processes

Answer 11

• Passive processes - do not require external source of energy such as ATP
• Simple diffusion
• Facilitated diffusion
• Osmosis
• Active processes - require external source of energy such as ATP
• Primary
• Secondary / co-transport
• Vesicular transport

Question 12

Define diffusion

Answer 12

• Diffusion is a passive process
• That involves the overall net movement of small molecules from a region of higher concentration to a lower concentration
• Down the concentration gradient, until equilibrium

Question 13

Define Facilitated Diffusion

Answer 13

• Facilitated diffusion is a passive process
• That involves the overall net movement of molecules/ions from a region of higher concentration to a lower concentration
• Down the concentration gradient across a partially permeable membrane
• Via channel or carrier proteins

FOR CHARGED, POLAR AND LARGE MOLECULES

Question 14

Define Osmosis

Answer 14

• Osmosis is a passive process
• That involves the overall net movement of water molecules
• From an area of high water potential to an area of low water potential down water potential gradient
• through a partially/selectively permeable membrane until equilibrium

Water travels freely across membranes through aquaporins.

Question 15

Describe what is meant by tonicity

Answer 15

Tonicity of a solution relates to how the solution influences the shape of body cells.
- Tonicity affects the movement of water across membranes

Question 16

Define Active Transport

Answer 16

• Active transport is an active process requiring ATP from respiration
• Which involves the movement of molecules/ions from an area of low concentration to a high concentration against the concentration gradient
• Across a cell membrane, using carrier proteins

Question 17

Describe the process of active transport across a cell membrane.

Answer 17

• Complementary molecule to be transported binds to the specific site of carrier protein
• ATP on the inside of the membrane directly bonds to a carrier protein and hydrolysed to form ADP and Pi(phosphate)
• Causing carrier protein to change shape and move molecule across membrane & release
• Pi ion is released causing carrier protein to go back to its original shape

Question 18

Define Co-transport

Answer 18

• Co-transport is the transport of one substance coupled with the transport of another substance across a semi permeable membrane
• Using a carrier protein
• Both molecules move in same direction against concentration gradient

Question 19

Explain how Co- transport is involved in the absorption of glucose in the small intestine

ROUGH DIAGRAM:

LUMEN OF ILEUM
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
EPITHELIAL CELL
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
BLOOD

Answer 19

• Na+ ions are actively transported out of epithelial cells into bloodstream by carrier protein using hydrolysis of ATP
• So lower conc of Na+ ions in epithelial cell than lumen Generateing a concentration gradient for Na+ ions from ileum into epithelial cell
• Na+ ions move in by facilitated diffusion in co transporter bringing glucose with it against its concentration gradient

Question 20

Outline what is meant by vesicular transport
GET DIAGRAM

Answer 20

Bulk Transport = required for large
molecules
* Exocytosis – the outward bulk transport of
molecules through the membrane
Vesicles containing materials fuse with the
membrane as secretion takes place
* Endocytosis – the inward bulk transport of
molecules through the membrane

A portion of the membrane engulfs a substance