Studying Cells

Question 1

Outline the role of organelles in the production, transport and release of protein from eukaryotic cells. 6 points

Answer 1

1. Nucleus contains DNA which contains code for protein
   2.ribosome produces protein
2. Mitochondria produce ATP
3. Vesicles transports it to Golgi apparatus
4. Golgi modifies, packages and stores protein
5. Vesicle transport protein to edge of cell
6. Vesicle fuses with cell membrane releasing the protein by exocytosis

Question 2

Describe differences between eukaryotic and prokaryotic cells. 7 points

Answer 2

1. Nucleotide structure identical
2. Phosphodiester bonds between adjacent nucleotides
3. Chloroplast DNA similar structure to prokaryotic DNA
4. Eukaryotic DNA is linear whereas prokaryotic DNA is circular
5. Eukaryotic DNA is associated with histones whereas prokaryotic DNA is not associated with histones
6. Eukaryotic DNA contains introns whereas prokaryotic DNA does not contain introns
7. Eukaryotic DNA is longer whereas prokaryotic DNA is short

Question 3

State three differences between DNA in nucleus of plant cell and DNA in a prokaryotic Cell.

Answer 3

1. Plant cells DNA linear whereas prokaryotic dna is circular
2. Plant cell dna is associated with histones whereas prokaryotic dna is not
3. Plant cell dna is longer whereas prokaryotic dna is short

Question 4

Describe how structure of cholera bacterium is different to structure of epithelial cell.

Answer 4

Cholera bacterium is a prokaryotic cell
Cholera bacteria does not contain membrane bound organelles
Eg endoplasmic reticulum
Cholera bacterium contains plasmid
Capsule
DNA held in a loop
70s ribosomes

Question 5

Advantage of TEM over SEM

Answer 5

Higher resolution
So smaller structures within the cell so can be seen

Question 6

Advantage of SEM over TEM

Answer 6

specimen does not have to be thinly sliced
Can be 3D

Question 7

Explain advantages and limitations of using a TEM to investigate cell structure.

Answer 7

1. Electrons have shorter wavelength
2. So higher resolution
3. So smaller structures within the cell can be seen
4. Specimen must be dead
5. Must be thinly sliced
6. Must be viewed in a vacuum
7. Preparation may create artefacts

Question 8

Explain why solution was isotonic, ice cold and buffer.

Answer 8

Isotonic- prevent osmotic effect so water doesn’t move into cell causing them to burst
Ice cold- prevent enzyme activity so cells don’t become damaged/ Broken down
Buffer- prevent PH changes so proteins don’t denature

Question 9

Describe how cell fractionation and centrifugation can be used to isolate mitochondria in a suspension of animal cells. 7points

Answer 9

1. Cell homogenisation break open cells releasing organelles
   *isotonic, ice cold, buffer solution used
2. Isotonic to prevent osmotic effect so water doesn’t move into cell causing them to burst
3. Ice cold to prevent enzyme activity so cells don’t become damage/ broken down
4. Buffer to prevent PH changes so proteins don’t denature
5. Filtered to remove debris
6. Place in centrifuge and spun at a high speed causing nuclear components to go into pellet
7. Remove and respin at a higher speed so mitochondria go into the pellet
8. Place under a microscope to observe mitochondria

Question 10

Describe the structure of phospholipid molecule and explain how phospholipids are arranged in a plasma membrane.3 points

Answer 10

1. Phospholipids have a glycerol, phosphate on one side and two fatty acid tails on the other
2. Fatty acid tails are hydrophobic and phosphate heads are hydrophilic
3. Forms phospholipid bilayer