Sub Cellular Structure: Prokaryotic Cells

Question 1

What are structures in prokaryotic cells that are not in eukaryotic cells? (7)

Answer 1

Cell wall, cell surface membrane, capsule, flagella, plasmids, inclusions, mesosomes

Question 2

What is the structure of a bacterial cell?

Answer 2

All bacterial cells have a cell wall, which is made up of murein- this is a polymer of polysaccharides and peptides. They further protect themselves by secreting a capsule of mucilaginous slime around this wall.
Cytoplasm contains 70s ribosomes.
Bacterial cells, the genetic material, is stored in a circular strand of DNA not contained in a nucleus. There are smaller circular pieces of DNA- plasmids. They can reproduce independently and give the bacterium resistance to harmful chemicals such as antibiotics. Plasmids are extensively used as vectors in genetic engineering

Question 3

How do bacterial cells store food?

Answer 3

Bacteria store food reserves as glycogen granules and oil droplets

Question 4

What is the structure and function of the cell wall?

Answer 4

Made from polysacchorides (not cellulose), including peptidoglycan/murein. Protects the cell from bursting; not permeable to proteins or nuclei acids.
It’s a physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis

Question 5

What is the structure and function of the cell surface membrane?

Answer 5

Semi-permeable; in-folds called mesosomes may contain enzymes for respiration and photosynthesis
Acts as a differential permeable layer, which controls the entry and exit of chemicals

Question 6

What is the structure and function of the capsule?

Answer 6

Protective layer of slime - prevents dehydration; for attachment to each other
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection

Question 7

What is the structure and function of the flagella?

Answer 7

For movement and allows chemotaxis - used for locomotion (only certain species)

Question 8

What is the structure and function of the bacterial chromosome?

Answer 8

Circular double-stranded DNA (not conatined in a nucleus)
Possesses the genetic information of the replication of bacteria cells

Question 9

What is the structure and function of plasmids?

Answer 9

Smaller pieces of circular DNA may contain genes for antibiotic resistance and pathogenicity. This aids in the survival of bacteria in adverse places

Question 10

What is the structure and function of the insclusions?

Answer 10

Glycogen and lipids - food reserves; other types of inclusions include protein crystals, which may act as toxins

Question 11

What is the structure and function of mesosomes?

Answer 11

Infloded regions of the cell surface where ATP production takes place

Question 12

what is the structure of the virus cell?

Answer 12

acellular non-living particles. they are smaller than bacteria. they contain nucleic acids DNA and RNA but can only multiply inside a living host cell. the nucleic acids are enclosed within a protein coat called the capsid. human immunodeficiency virus is surrounded by a lipid envelope. both have attachment proteins which are essential to allow the virus to identify and attach to a host cell

Question 13

what can viruses called bacteriophages do?

Answer 13

they can infect and set in motion a genetic takeover of bacteria e.g. Escherichia coli

Question 14

what do viral genomes maybe consist of?

Answer 14

double or single-stranded DNA
double or single-stranded RNA

Question 15

what do some viruses have and what are they made from?

Answer 15

some viruses have envelopes which are membranous coverings derived form the membrane of the host cell

Question 16

what is a host range?

Answer 16

a limited number of host cells that the virus can infect

Question 17

what do viruses use in host cells?

Answer 17

viruses use enzymes, ribosomes, and small molecules of host cells to synthesize progeny viruses

Question 18

what do viral glycoproteins on the envelope do?

Answer 18

the glycoproteins bind to specific receptor molecules on the surface of the host cell

Question 19

what do retroviruses use the enzymes reverse transcriptase for?

Answer 19

to copy their RNA genome into DNA, which can then be integrated into the host genome as a provirus

Question 20

what is cell fractionation?

Answer 20

is a process where cells are broken up and the different organelles they contain separate out

Question 21

why is the tissue placed into a cold, isotonic, and buffered solution before cell fractionation?

Answer 21

• reduced enzyme activity which may break down organelles
• same water potential inside and outside the cell to prevent organelles bursting/shrinking from osmotic gain/loss of water
• buffered to maintain a constant PH in order to prevent organelle proteins, including enzymes, from becoming denatured

Question 22

what is the process of ultracentrifugation?

Answer 22

1) tissue to be studied is cut into small pieces (minced) and placed into a cold, isotonic, and buffered solution
2) these are then ground into smaller pieces using a homogeniser (sophisticated liquidiser) to release the organelles from the cell
3) the homogenate is filtered to remove any complete cells and large debris e.g. cell wall/membrane
4) a suspension of homogenate is then placed in a test tube and then centrifuged - the faster the speed at which the tube is spun.-, the greater the force generated
5) at slower speeds the larger fragments collect at the bottom of the test tube and smaller ones remain near the top suspended in a liquid called the supernatant liquid
6) these larger fragments (sediment pallets) are then removed and the supernatant remaining is re-spun at a faster speed (more force) and some of the smaller fragments collect at the bottom forming a new pallet
7) by continuing in this way smaller and smaller fragments will be removed

Question 23

what is the reproduction of an HIV cell?

Answer 23

HIV binds to CD4 antigens on CD4 T helper cells
membrane empties contents into the cell
reverse transcription enzyme acts on internal RNA, crating double-stranded cDNA
cDNA becomes part of the host DNA
host transcribes DNA forming new viral particles making up capsid, more enzymes and RNA

Question 24

what is the reproductive cycle of an enveloped RNA virus?

Answer 24

1) glycoproteins on the viral envelope bind to specific receptor molecules (not shown) on the host cell, promoting viral entry into the cell
2) capsid and viral genome enter the cell
3) the viral genome functions as a template for synthesis of complementary RNA strands by a viral enzyme
4) new copies of viral genome RNA are made using complementary RNA strands as templates
5)complementary RNA strands also function as mRNA which is translated into both capsid proteins (in the cytosol) glycoproteins for the viral envelope (in the ER)
6) vesicles transport envelope glycoproteins to plasma membrane
7) a capsid assembles around each viral genome molecule
8) new virus