3.2.1 Cell structure

Question 1

What happens during Homogenation?

Answer 1

Cells broken open (by a homogeniser/blender) to release organelles

Question 2

List the 3 heaviest organelles

Answer 2

1) nucleus
2) chloroplasts (plants)
3) mitochondria

Question 3

Why is homogenate filtered?

Answer 3

To remove complete cells/ large cell debris

Question 4

How are prokaryotic cells different to eukaryotic cells

Answer 4

• No membrane bound organelles/No endoplasmic reticulum, nucleolus, lysosomes or Golgi apparatus
• Chromosomes are shorter, circular loop of DNA, not associated with proteins
• Smaller 70s ribosomes
• Murein cell wall
• Much smaller

Question 5

What is the structure and function of the nucleus?

Answer 5

• Contains genetic material - necessary to control cells activities
• Surrounded by double membrane - nuclear envelope. Contains nuclear pores to allow large molecules like mRNA out and into cytoplasm.
• Contains chromosomes with protein-bound, linear DNA
• Filled with nucleoplasm
• Nucleolus makes rRNA which is made into ribosomes

Question 6

What are lysosomes?

Answer 6

Vesicles/membrane bound organelle that releases hydrolytic (digestive) enzymes like proteases, lipases, carbohydrases.

Question 7

What are similarities between prokaryotic and eukaryotic cells?

Answer 7

• Both have DNA
• Both have cell-surface membrane
• Both have cytoplasm
• Both have ribosomes

Question 8

Describe process of ultracentrifugation

Answer 8

1. Break open/grind cells/tissue and filter
2. In cold, same water potential/concentration, pH
   controlled solution
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts (e.g.) settle out

Question 9

In cell fractionation, why is the tissue placed in a cold, buffered, isotonic solution?

Answer 9

Cold: reduce activity of enzymes which may break down organelles (not cells)

Buffered: to maintain constant pH so enzymes aren’t denatured

Isotonic: to stop organelles bursting/shrinking due to osmotic gain/loss of water

Question 10

What is cell fractionation?

Answer 10

The process where cells are broken up and the organelles they contain are separated out

Question 11

What are the 2 types of ribosomes?

Answer 11

70s in prokaryotic cells
Larger 80s in eukaryotic cells

Question 12

What is homogenate?

Answer 12

Fluid containing the organelles, cell membrane and cells

Question 13

Describe the structure and function of mitochondria

Answer 13

• double membrane
• inner membrane folds into cristae
• fluid inside called matrix
• production of ATP (oxidative phosphorylation)

Question 14

What is the function of the Golgi apparatus?

Answer 14

Modifies, processes and packages (proteins) into vesicles for transport

Question 15

Describe the structure and function of the rough and smooth endoplasmic reticulum

Answer 15

• Both have membranes that surround flattened sacs called cristernae
• Rough endoplasmic reticulum has membrane bound ribosomes (site of protein synthesis)
• Transports newly synthesised proteins to Golgi apparatus through vesicles
• Smooth endoplasmic reticulum synthesises, stores and transports lipids

Question 16

Describe the structure of a chloroplast

Answer 16

• double membrane- controls what enters and leaves the cell
• granum - stack of thylakoids (light absorbed more efficiently)
• thylakoids - membrane bound flattened sacs (contains enzymes and chlophyll needed for light dependent reactions)
• lamellae- allows chemicals to pass between grana
• stroma - fluid in chloroplast (site of light independent reactions)

Question 17

How can the structure of a chloroplast change to reduce the RATE of photosynthesis?

Answer 17

• less thylakoid membrane
• smaller surface area
• less chlorophyll so reduced light absorption