BIO 204 Lecture 6 — Bacterial Genetics

What do all organisms use to encode their genome?

DNA.

What are nucleic acids made of?

Chains of nucleotides.

What bases are found in DNA?

Adenine (A), guanine (G), cytosine (C), and thymine (T).

How is RNA different from DNA according to the lecture?

Uracil (U) replaces thymine (T), and RNA usually exists as single-stranded molecules.

What are proteins made of?

Peptide/polypeptide chains of amino acids.

What makes the 20 amino acid types different from one another?

Their side chains.

What is the primary structure of a protein?

The sequence of amino acids connected by peptide bonds.

Nucleic acids are made of what, while proteins are made of what?

Nucleic acids → nucleotides; proteins → amino acids.

What are the main characteristics of most bacterial chromosomes?

They are circular, double-stranded DNA chromosomes.

Where is the bacterial chromosome condensed?

In the nucleoid.

How is bacterial DNA condensed into the nucleoid?

By supercoiling.

What makes the bacterial genome compact?

Protein-coding sequences make up the majority of the genome.

How are bacterial genes often arranged?

In operons.

What is an operon?

Multiple genes lined up head-to-tail and controlled by a single promoter.

What is a plasmid?

A small piece of DNA that can be passed among bacteria and usually contains a set of related genes.

What types of genes can plasmids contain?

Virulence factors and antibiotic-resistance genes.

Multiple genes controlled by one promoter = ?

An operon.

What are the two main characteristics of bacterial DNA replication?

Semiconservative and bidirectional.

What does semiconservative replication mean?

Each daughter receives one original parental strand and one newly synthesized daughter strand.

If a new DNA molecule contains one old strand and one new strand, what type of replication occurred?

Semiconservative replication.

What does bidirectional replication mean?

Replication enzymes move in both directions from the origin.

Where does bacterial DNA replication begin?

At the origin of replication.

What happens to the DNA double helix when replication begins?

It is unwound.

What enzyme complex is loaded at the two replication forks?

DNA polymerase.

What helps correct mistakes made during DNA replication?

Constant proofreading repairs mistakes of DNA polymerase.

What happens to the newly completed daughter strand?

It is methylated to indicate that it is complete and ready for a new round of replication.

What happens after bacterial DNA replication is complete?

The cell divides, and the cycle repeats.

What are the two main steps of bacterial gene expression?

Transcription of DNA into mRNA and translation of mRNA into protein.

DNA → mRNA is called what?

Transcription.

mRNA → protein is called what?

Translation.

What performs transcription?

RNA polymerase.

Where does RNA polymerase bind to begin transcription?

A promoter.

What performs translation?

The ribosome.

What carries specific amino acids to the ribosome?

tRNA.

What does the ribosome do?

Reads one codon at a time and adds a single amino acid to the growing peptide chain.

When do replication and gene expression occur in growing bacteria?

They occur simultaneously.

Where do transcription and translation occur in bacteria?

In the same cellular compartment.

What does it mean that bacteria couple transcription and translation?

Translation begins before transcription has ended.

Why can bacteria couple transcription and translation?

Because they occur in the same compartment.

When can ribosomes begin translating an mRNA?

As soon as the 5′ end of the mRNA emerges from RNA polymerase.

What does bacterial RNA polymerase interact with during transcription?

A sigma factor.

RNA polymerase + sigma factor form what?

The holoenzyme.

What does the holoenzyme do?

Loosely binds DNA and scans for a promoter sequence.

Why are there multiple types of sigma factors?

Different sigma factors have different target genes.

What happens to the sigma factor after transcription begins?

It is released.

If RNA polymerase needs to locate a promoter, what protein does it interact with?

A sigma factor.

Why do bacteria regulate gene expression?

To avoid expressing unnecessary proteins and wasting energy.

What determines when specific bacterial genes are activated?

Environment, metabolism, growth phase, and other conditions.

At what levels can bacterial gene expression be regulated?

DNA level, transcriptional control, translational control, and post-translational modifications.

How can bacteria regulate expression at the DNA level?

By flipping promoter sequences to change the DNA code and control downstream genes.

How can bacteria regulate transcription?

Using alternative sigma factors, activators, and repressors.

How can bacteria regulate translation?

Translational repressors can bind mRNA and block ribosome binding.

How can bacteria regulate proteins after translation?

Proteins can be cleaved, folded, phosphorylated, methylated, etc. to alter their activity and function.

What are global regulators?

Proteins that affect the expression of many different genes.

What type of signals do global regulators respond to?

Internal signals.

What does cAMP signal to the bacterial genome?

That the cell needs more carbon and energy.

What happens when CAP binds cAMP?

The CAP-cAMP complex can bind DNA promoters and induce expression of many genes involved in metabolic pathways.

What type of signals do two-component signaling systems respond to?

External signals.

What are the two components of a two-component signaling system?

Sensor kinase and response regulator.

What does the sensor kinase do?

Detects specific signal molecules or conditions outside the cell.

What does the response regulator do?

It is activated in the cytoplasm and binds DNA promoters to alter gene expression.

Global regulator vs. two-component system: what is the major signal difference?

Global regulators → internal signals; two-component systems → external signals.

Semiconservative

One old strand + one new strand

Bidirectional

Both directions from origin

DNA polymerase

Replication

RNA polymerase

Transcription

Ribosome

Translation

Operon

Multiple genes + one promoter

Sigma factor + RNA polymerase

Holoenzyme

Sigma factor

Helps locate promoter/targets genes

Global regulator

Internal signals

Two-component system

External signals

Sensor kinase

Detects outside signal

Response regulator

Alters gene expression