🧬 Chapter 8: Microbial Genetics – Part 1 Study Guide

What is a genome?

All the genetic material in a cell, including chromosomes and plasmids; the full set of hereditary instructions.

What is a gene?

A segment of DNA that encodes a functional product, usually a protein or RNA molecule.

What is the difference between genotype and phenotype?

Genotype is the complete set of genes or genetic makeup of an organism, while phenotype is the observable traits or characteristics of an organism.

What does DNA consist of?

DNA is made of nucleotides, each containing a phosphate group, a deoxyribose sugar, and a nitrogenous base (A, T, G, C).

What is the function of DNA?

Stores hereditary information and allows faithful replication.

What are the steps of bacterial DNA replication?

1. Topoisomerase & Gyrase relax supercoiled DNA

2. Helicase unwinds the DNA strands 

3. SSB Proteins stabilize open strands

4. Primase synthesizes RNA primers

5. DNA Polymerase III adds new nucleotides

6. DNA Polymerase I replaces RNA primers with DNA

7. Ligase joins Okazaki fragments

What is the leading strand in DNA replication?

The strand that is synthesized continuously toward the replication fork.

What is the lagging strand in DNA replication?

The strand that is synthesized in short fragments (Okazaki fragments) away from the fork.

What is the Central Dogma of Life?

DNA → RNA → Protein; where DNA copies itself, DNA makes RNA, and RNA builds proteins.

What is the purpose of the Transcription Process?

To create mRNA from a DNA template.

What is Initiation (Transcription Process)?

The first step in transcription, where RNA polymerase binds to the promoter DNA region.

What is Elongation (Transcription Process)?

The second step, RNA polymerase adds complementary RNA bases to the growing mRNA strand.

What is Termination (Transcription Process)?

The third step, transcription stops when RNA polymerase reaches a stop signal, causing the mRNA strand to be released.

Where does transcription occur in prokaryotes?

In prokaryotes, transcription occurs in the cytoplasm.

Where does transcription occur in eukaryotes?

Nucleus

What types of RNA are there?

mRNA (Messenger RNA), tRNA (Transfer RNA), rRNA (Ribosomal RNA).

What is a codon?

A 3-base sequence on mRNA coding for an amino acid.

What is an anticodon?

A complementary 3-base sequence on tRNA that pairs with the codon.

What is the function of a promoter?

It marks the starting point for transcription. It controls when and where a gene is expressed.

What is an operon?

A cluster of genes controlled by a single promoter and operator, acting as a unit.

What are the main parts of the lac operon?

Regulator gene, Promoter, Operator, Structural genes.

How does the lac operon function when lactose is present?

Lactose binds to the repressor, releases it from the operator, and allows transcription to occur.

What is the function of mRNA (Messenger RNA)?

mRNA carries genetic code from DNA to the ribosome for protein synthesis.

What is the function of tRNA (Transfer RNA)?

tRNA brings specific amino acids to the ribosome during translation.

What is the function of rRNA (Ribosomal RNA)?

rRNA forms the structural and catalytic core of ribosomes and catalyzes peptide bond formation.

What is the Start Codon?

AUG (Methionine)

What are the Stop Codons?

UAA, UAG, UGA

What is Helicase?

The enzyme that unwinds the DNA strands during replication.

What is DNA Polymerase III?

The enzyme that adds new nucleotides (5' \rightarrow 3') to a growing DNA strand during replication.

What is Ligase?

The enzyme that joins Okazaki fragments on the lagging strand.

What is Semiconservative Replication?

The process where DNA produces two identical DNA molecules, each consisting of one original (old) strand and one newly synthesized strand.

What is the base pairing rule in DNA?

Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds; Guanine (G) pairs with Cytosine (C) via 3 hydrogen bonds.

How are DNA strands oriented?

DNA strands run antiparallel, meaning they orient in opposite directions (5'→3' and 3'→5').

What is the function of the Promoter, Start Codon, and Ribosome Sites (A, P, E)?

These sites ensure smooth and accurate protein assembly.

What is a Promoter?

DNA region where RNA polymerase binds to start transcription.

What is a Start Codon?

First codon on mRNA to begin translation.

What is the A Site (Aminoacyl)?

New tRNA enters.

What is the P Site (Peptidyl)?

Growing peptide chain held here.

What is the E Site (Exit)?

Used tRNA exits the ribosome.

What is the function and advantage of an operon?

An operon regulates the expression of related genes as a unit, which saves energy by turning genes ON only when needed.