Review of General Bacterial Genetics Concepts

Question 1

describe the structure of the bacterial genome (4)

Answer 1

1. shape: one long single molecule of double-stranded, helical, supercoiled DNA that FORMS A PHYSICAL CIRCLE;
   very few bacterial exceptions have linear genome (ex. Borrelia, the bacterium that causes lyme disease)
2. haploid: only one copy of all genes
3. NOT membrane-bound
4. some bacteria have plasmids: circular DNA molecules capable of autonomous replication: smaller than the genome, vary in copy number, and vary in size, but several are transmissible and many encode virulence factors and/or antibiotic resistance

Question 2

explain the steps in bacterial DNA replication (4)

Answer 2

1. uncoil the helix via DA helicases
2. separation of the strand by breaking hydrogen bonds between the complementary bases
3. DNA polymerase synthesizes 2 new strands by complementary nitrogenous base pairing
4. DNA gyrase restores supercoiled form

Question 3

what are the 7 parts of gene specifying proteins?

Answer 3

1. promoter region
2. transcriptional start site (mRNA)
3. ribosome binding site
4. translational start codon
5. open reading frame/protein coding sequence
6. translational stop codon
7. transcriptional stop site

Question 4

what is an operon?

Answer 4

multiple consecutive genes under transcriptional control of the same promoter, all genes are transcribe as one block at the same time; have only one promoter region, only one transcriptional start site, but can have multiple open reading frames

Question 5

describe standalone transcriptional units

Answer 5

units with their own promoter regions, their own transcriptional start sites, and their own open reading frames

Question 6

describe a regulon

Answer 6

promoters bind the same regulatory factor(s) which allow genes to be transcribed at the same time and/or under the same conditions even though they are physically UNLINKED in the genome

Question 7

how is mRNA organized?

Answer 7

divided up into codons (3 nucleotides coding for one specific amino acid; one amino acid can be specific by multiple different codons)

Question 8

describe the bacterial ribosome

Answer 8

2 subunits:

1. 30S
2. 50S: has 3 sites
   A: acceptor: where loaded tRNA first attaches
   P: peptide: temporary holding site for growing peptide
   E: exit: uncharged tRNA released from ribosome

both come together to form 70S ribosome which translates mRNA into proteins

Question 9

describe the process of how bacterial genes are used to make proteins (transcription and translation)

Answer 9

1. transcription of bacterial DNA into RNA: the product of a gene is rRNA, tRNA, or mRNA; RNA is synthesized by complimentary nitrogenous base-pairing or ribonucleotides with deoxyribonucleotides by RNA polymerase; DNA is unwound, creating a region of non-paired deoxyribonucleotides that serve as a template for RNA synthesis (similar to replication, just different substrates)
2. translation of bacterial mRNA into protein: translation is initiated by the binding of the 30S subunit to the ribosome binding site on the mRNA and recruits the 50S subunit (translational subunit); ribosome moves alone mRNA until it reaches the translational start codon, translates the ORF into proteins until it reaches the translational stop codon and the ribosome disassembles

Question 10

describe the means by which bacteria generate genetic diversity (2)

Answer 10

via spontaneous mutation, which is accomplished via

1. point mutation: affects only one nucleotide
2. insertion or deletion of large DNA fragments: usually involves a transposon or insertion sequence, these are mobile genetic elements that can insert themselves anywhere and can lead to spontaneous deletion of large fragments of DNA from the genome

OR via acquisition of new DNA material via:
1. natural transformation
2. conjugation
3. transduction

Question 11

list and describe the 4 point mutations

Answer 11

1. silent: changing the nucleotide has no effect; the original intended amino acid is still produced
2. nonsense: changing the nucleotide results in an accidental stop codon and disrupts translation
3. missense:
   3a. conservative: changing the nucleotide results in changing the amino acid produced, but the amino acid produced is somewhat related to the originally intended amino acid
   3b. non-conservative: changing the nucleotide results in changing the amino acid produced, and the produced AA is entirely unrelated to the originally intended AA

Question 12

describe natural transformation, conjugation, and transduction as acquisition of new genetic material

Answer 12

natural transformation: uptake of naked DNA; bacteria die, lyse, and release their DNA and other bacteria pick up the DNA and incorporate it into their DNA (can also pick up plasmids)

conjugation: using a pilus to transfer a plasmid from a donor bacteria to a recipient bacteria

transduction: DNA injected into bacteria (by a bacteriophage); viral DNA integrated into the bacterium genome

all 3 can lead to novel traits such as antibiotic resistance, toxins, or virulence factors

Question 13

list 9 key differences between eukaryotes and bacteria

Answer 13

1. bacteria are unicellular, euk are multi
2. bacteria have cell wall, euk don’t
3. bacteria cytoplasm does not contain membrane-bound organelles, euk does
4. bacteria have circular genome, euk have linear genome
5. bacteria genome is not surrounded by a membrane (nucleus), euk is
6. in bacteria, transcription and translation are coupled; they are not in euk
7. in bacteria, genes do not have introns or exons, in euks they do
8. bacteria genome is haploid, euk is diploid
9. in bacteria plasmids are common; but plasmids are rare in euk