bacteria

Question 1

what to include in drawing a baterium

Answer 1

capsule, cell wall, cytoplasm, cell membrane, circular DNA (distinctive feature), plasmid, fimbriae, sex pilli, flagellum

Question 2

what are the points of comparison between bacterial and eukaryotic chromosome (7)

Answer 2

size, appearance, association with proteins, location, presence of extrachromosomal DNA, presence of intron, presence of operon

Question 3

what is the role of plasmid

Answer 3

• used EXTENSIVELY in genetic engineering as vectors for carrying and expressing foreign DNA in bacterial cells

Question 4

describe plasmids

Answer 4

they are a SMALL, CIRCULAR autonomously replicating DNA molecule

Question 5

explain the function of cell wall in bacteria

Answer 5

1. protects the cell from osmotic lysis
2. confers rigidity and shape to cell

Question 6

describe the cell wall structure

Answer 6

consists of a polymer called peptidoglycan: long chains of sugars cross-linked by short peptide chains

Question 7

describe capsule

Answer 7

some bacteria have a layer of polysaccharides known as glycocalyx to the exterior of the cell wall

the glycocalyx can be a distinct layer: that exists as a diffused mass known as the slime layer

Question 8

function of capsules

Answer 8

1. protects the bacteria from being taken in via phagocytosis by the phagocytes which are unable to recognise the bacteria due to the capsule
2. enables bacteria to adhere to one another/surfaces
3. prevent desiccation of bacteria, as it contains water to prevent the bacteria from drying out

Question 9

differences between binary fission and mitosis

Answer 9

end product, amount of DNA, DNA replication, behaviour of chromosomes, spindle fibres

Question 10

why is binary fission beneficial

Answer 10

being genetically identical is a selective advantage in a stable, favourable environment as it allows successful genotypes to rapidly colonise a habitat

Question 11

key points to mention when describing binary fission

Answer 11

1. ori of replication, unzipping by breaking hydrogen bonds between bases of 2 strands –> replication bubble
2. semi-conservative replication, template/strand, CBP
3. new ori formed, opposite poles, attached to membrane
4. elongates –> division
5. with no free ends, circular, interlocked
6. toposomerase, cut, separate, reseal
7. invagination of plasma membrane, divide, complete genome

Question 12

define transformation

Answer 12

uptake of naked, foreign DNA fragements from the surrounding environment, changing the bacterial cell’s GENOTYPE and PHENOTYPE

Question 13

how can bacterial cells be made artificially competent

Answer 13

immersion in a culture medium with high concentrations of calcium chloride followed by a heat shock treatment (to introduce foreign genes into the E. coli genome by making more transient pores)

Question 14

define transduction

Answer 14

process by which the bacterial DNA from one host cell is introduced into another bacterial cell by a bacteriophage due to aberrations in the phage reproductive cycle

Question 15

what happens if there is no crossing over between homologous regiosn between the foreign DNA and bacterial chromosome

Answer 15

foreign DNA will be degraded

Question 19

How is foreign DNA incorporated into the host cell chromosome

Answer 19

Crossing over at the homologous regions on the bacterial chromosomes —> a recombinant is formed

Question 20

When would a cell be called to have transformed

Answer 20

Crossing over at the homologous regions thus different alleles are exchanged and NEW allele is expressed, genotype and phenotype have PERMANENTLY changed

Question 21

Explain how does the rolling circle DNA replication take place

Answer 21

1. One dsDNA strand is nicked by nuclease
2. The nicked 3’OH end acts as a primer for strand elongation by DNA polymerase using the intact strand as the template for synthesis of a complementary strand —> dsplasmid
3. Facilitated by the displacement of the 5’ end
4. Transferred across the cytoplasmic mating bridge to the recipient bacterium
5. Another nick occurs to release the original strand upon completition of a unit length of the plasmid DNA
6. The ss F plasmid DNA re-circularises and serves as template for the synthesis of a complementary DNA strand —> ds F plasmid

Question 22

What’s the benefit for bacteria to regulate its genes

Answer 22

• allows the economic use of energy and resources such that the gene is expressed and protein produced only when necessary
• respond appropriately and rapidly to environmental changes

Question 23

Describe the lac operon

Answer 23

• three strucrtural genes arranged in the sequence lac Z, lac Y and lac A
• lac Z: beta-galactosidase, lac Y: permease; lac A: transacetylase
• operator located between the promoter and the structural genes control the transcription of the structural genes by controlling ACCESS of RNA polymerase
• a short distance upstream of the operon is its regulatory gene, lacI (HAS ITS OWN PROMOTER AND TERMINATOR SEQUENCES)`

Question 24

Describe the default operation of the lac operon

Answer 24

1. LacI is constitutively transcribed, continued production, repressor p
2. Active form, binds, operator, DNA binding site
3. Absence of lactose, denying RNA polymerase
4. Block transcription of structural genes, switch off

Question 25

Keywords when describing the induced reaction of lactose

Answer 25

1. Permease, beta galactosidase, also lactose
2. Allosteric site, inactivate repressor, altering tertiary structure, repressor, DNA-binding site, no longer complementary
3. RNA polymerase, access and bind to promoter
4. Structural genes transcribed as a single polycistronic mRNA

Question 26

Positive regulation of lac operon

Answer 26

1. Glucose, cAMP levels
2. Binds to the allosteric site of CAP, CAP-cAMP complex, activating CAP —> binds to CAP binding site within the promoter
3. Increases affinity of the promoter region for RNA polymerase, rate of transcription initiation
4. Structural genes transcribed, polycistronic mRNA