Chapter 10: Microbial Genetics

Question 1

Genetics

Answer 1

Study of inheritance and inheritable traits

Question 2

Genome

Answer 2

The entire genetic complement of an organism

Question 3

Ploidy

Answer 3

The number of sets of chromosomes in the nucleus of a biological cell

Question 4

Genotype

Answer 4

Set of genes in an organism

Question 5

Phenotype

Answer 5

Physical and functional traits of an organism

Question 6

Transcription

Answer 6

The process by which genetic information represented by a sequence of DNA nucleotides is copied into newly synthesized molecules of RNA, with the DNA serving as a template.

Question 7

Translation

Answer 7

The process by which a sequence of nucleotide triplets in a messenger RNA molecule gives rise to a specific sequence of amino acids during synthesis of a polypeptide or protein.

Question 8

Polycistronic

Answer 8

A description of mRNA that encodes for multiple polypeptides

Question 9

Gene

Answer 9

A hereditary unit of information

Question 10

Compare the structure of prokaryotic and eukaryotic genomes.

Answer 10

Eukaryotes: Larger, more complex, linear chromosomes in nucleus, generally diploid, introns and exons, histones.

Prokaryotes: Smaller, less complex, singular circular chromosome in the nucleoid and sometimes plasmids, haploid, lacks introns.

Question 11

Discuss the structure of DNA.

Answer 11

-Double helix that holds stable genetic information in the sequence of bases
-Lives in the nucleus of eukaryotic cells and the nucleoid of prokaryotic cells
-Replicates itself to be passed on generation to generation of cells/many viruses
-Transcribed to RNA

Question 12

Discuss the central dogma of genetics; DNA replication, transcription & translation. Discuss the properties of DNA that facilitate these processes. Describe these processes.

Answer 12

Look up image

Question 13

Utilize the coding strand of a gene to generate the template strand, mRNA, and amino acid sequence.

Answer 13

Work practice problem

Question 14

Distinguish between genotype and phenotype.

Answer 14

Genotype: The entire genetic complement of an organism

Phenotype: The physical and functional traits of an organism

Governed by genotype, gene expression, translational controls, and post-translational modification

Question 15

Compare and contrast inducible operons and repressible operons.

Answer 15

Promoters
Sequences upstream of gene to which RNA polymerase binds
With help of sigma factor in prokaryotes
With help of initiation factors in eukaryotes
Operons
Genetic sequences led by single promoter containing multiple genes and an operator, controlled by a single regulatory gene

Inducible vs repressible: turning on and off
Inducible systems start “off” and are turned “on” by inducers
Repressible systems start “on” and are turned “off” by repressors
Positive vs. negative: increasing or decreasing gene expression
Positive control systems make use of an enhancer/activator to increase gene expression
Negative control systems make use of repressor to reduce gene expression
Some operons can be under both positive and negative control

Question 16

Describe the different mechanisms of genetic transfer.

Question 17

Compare the 3 types of horizontal genetic transfer discussed in lecture.

Answer 17

Introduces genetic variation to what would otherwise be clones

Transfer of genes from one independent, mature organism to another

Donor cell/microbe contributes part of genome to recipient cell

Genes can be transferred to the same or different species

Sometimes microbe-directed, sometimes directed by external factors

3 types:
Conjugation
Transformation
Transfection

Question 18

Discuss plasmids

Answer 18

Smaller, autonomously replicating, circular pieces of DNA are called plasmids.

Typically confer advantages – resistance to antimicrobials, virulence factors, etc.

Not necessary for metabolism, growth, reproduction.

DNA is wrapped around histones in Archaea and Eukarya– proteins that help compact DNA and play a role in gene regulation. Looped in bacterial cells – no histones.

Question 19

DNA Replication

Answer 19

Circular genome:
Ori – origin of replication, specific site within genome where DNA polymerase will bind to start replication
Can have multiple
Synthesis proceeds in both directions – bidirectional

DNA helicase – enzyme that breaks the DNA helix and opens it up so replication machinery can access the strands

Intersection of open strands is called a replication fork

DNA polymerase III – version that bacteria use to synthesize DNA strands

Leading strand

Continuous replication 5’ to 3’

Lagging strand

Non-continuous – enzyme called primase must first lay down RNA primer to provide a 3’ hydroxyl for DNA polymerase to bind and start adding more nucleotides

DNA polymerase I replaces primers between Okazaki fragments and ligase repairs nicks

Question 20

DNA Transcription

Answer 20

Eukaryotes:
In nucleus
Requires multiple molecular factors
Multi-step process
pre-mRNA synthesis
Modified guanine capping
Polyadenylation
Splicing

Prokaryotes:
In nucleoid
Made for efficiency
No introns
Formylmethionine (f-Met)
Multiple transcripts from same gene → different proteins (polycistronic)
Multiple RNA polymerases working simultaneously

Question 21

Translation

Answer 21

Ribosomes attach to growing transcripts in prokaryotes – all about efficiency

Small subunit binds first, then large subunit
Use codons (sets of three nucleotides) as “code” for specific amino acids

Pretty consistent among domains of life – some differences

See similarities among prokaryotes, mitochondria, and chloroplasts in amino acids
tRNA – transfer RNA

Anticodon is complement of codon
tRNA “charged” with amino acid
“Wobble” position and redundancy

Question 22

Review mutations slides

Answer 22

/

Question 23

Transformation

Answer 23

Mechanism: A competent bacterial cell takes up “naked” (free) DNA fragments from its environment.

Origin of DNA: The DNA is released by dead or lysed cells.

Examples: Acquiring genes that confer antibiotic resistance from the environment.

Question 24

Transduction

Answer 24

Mechanism: A bacteriophage (virus) accidentally packages bacterial DNA instead of its own viral DNA during replication.

How it works: The virus then infects a new bacterium, injecting the previously acquired bacterial DNA into the recipient cell.

Examples: Transfer of genes, such as those encoding toxins or virulence factors, via a virus.

Specialized transduction:
Only certain donor DNA sequences

Question 25

Conjugation

Answer 25

Mechanism: Requires direct, intimate contact between a donor cell and a recipient cell, often facilitated by a specialized pilus. How it works: The donor cell forms a bridge with the recipient cell and transfers genetic material, such as a plasmid, which often carries advantageous genes like those for antibiotic resistance. Examples: Rapid spread of antibiotic resistance genes between bacteria through direct physical contact.