BIOL 251 Microbiology Week 11 Lecture Notes

Microbiology: An Introduction 13th Edition - Ch. 8 - 9

Genetics

The study of how traits and characteristics are passed from one generation to the next through DNA.

Focuses on how microbes inherit, express, and mutate genes.

Chromosomes

Structures made of DNA and proteins (mostly histones in eukaryotes) that carry genetic information.

Bacteria typically have a single circular chromosome, while eukaryotic cells have multiple linear chromosomes.

Genes

Specific segments of DNA that code for proteins or functional RNA. Each gene is a unit of heredity and determines particular traits or functions

Genome

The entire set of genetic material in an organism.

Includes chromosomes, plasmids (in bacteria), and any other genetic elements.

Genetic Code

The set of rules by which the sequence of nucleotides in DNA or RNA is translated into the amino acid sequence of proteins.

DNA

AKA Genetic blueprint

2 functions

• Double helix backbone

• Antiparallel strands

• Sugar phosphate backbone

• Two strands held by hydrogen bond

Central Dogma

The theory that genetic information flows from DNA to RNA to protein

Single circular chromosome

Short tandem repeats

Composed of DNA and protein

_____ _____ _____: Repeating sequences of non-coding DNA

Vertical

Horizontal

_____ Gene Transfer: Flow of genetic information from one generation to the next

_____ Gene Transfer: Transfer of genes between cells of the same generation

DNA Polymerase

Okazaki

ligase

Adds nucleotides to the growing DNA strand during DNA replication. Goes in the 5’ → 3’ direction

• initiated by RNA primer

• Leading strand is synthesized continuously

• Lagging strand is synthesized discontinuously, creating _____ fragments

• DNA Polymerase removes RNA primers, Okazaki fragments are joined by DNA _____

bidirectional

In prokaryotes, DNA replication is _____: occurs in two opposite directions from a single origin of replication

rRNA

tRNA

mRNA

_____: Integral part of ribosomes

_____: Transports amino acids during protein synthesis

_____: Carries coded information from DNA to ribosomes

Terminator

Transcription in Prokaryotes

• Synthesis of complementary mRNA strands

• RNA polymerase

• Promotor

• _____

• Proceeds in the 5’ → 3’ direction

Translation

When mRNA is translated into the “language” of proteins

• Codons

  • 61 sense codons - 20 amino acids

    • 1 start codon - AUG

• 3 nonsense codons - UAA, UAG, UGA

Ribosomes

Initiation, Elongation, Termination

What is the site of translation?

• tRNA

  • anticodon

What are the 3 steps involved?

A

P

E

Ribosomes have 3 binding sites for tRNA

___ Site: The entry point on the ribosome for a new tRNA carrying an amino acid.

It matches the anticodon of the tRNA with the codon on the mRNA strand.

___ Site: Holds the tRNA with the growing polypeptide chain.

The amino acid from the A site is joined to the chain here by a peptide bond.

___ Site: Where the empty tRNA (after it has donated its amino acid) is moved before it exits the ribosome.

fixed

inducible, repressible

Regulation of Bacterial Gene Expression

• Constitutive genes are expressed at a fixed rate

  • Not under control

  • Enzymes involved in glycolysis

• Other genes are expressed as needed

  • _____ genes and _____ genes

  • Control mechanism: Induction and Repression

    • Regulates transcription of mRNA

Promoter

Segment of DNA where RNA polymerase initiates transcription of structural genes

Operator

Segment of DNA that controls transcription of structural genes

Structural Genes

Region of DNA that codes for specific protein

Mutation

Mutagen

Spontaneous

A permanent change in the base of sequence DNA

May be neutral, beneficial, or hamrful

_____: Agents that cuase mutations

_____ mutation: Occur in absence of mutagens

Point

Frameshift

_____ mutation: Change only one base pair

Base substitions

• Silent, Missense, Nonsense mutations

_____ mutation: Insertion or deletion of one or more nucleotide pairs

• Shifts the translational “reading frame”

Silent

Missense

Nonsense

_____ mutation: Normal protein

• Does not change amino acid sequence

_____ mutation: Faulty protein

• Amino acid is changed

_____ mutation: Incomplete protein

REsults in stop codon

Chemicals

Radiation

What are some mutagens?

Nucleotide

Direct

DNA Repair

1. Proofreading

   • DNA Polymerase

2. Mismatch pair

   • Exonuclease

   • DNA Polymerase

   • Ligase

3. Repair of thymine dimers

   • _____ Excision repair: DNA polymerase, ligase

   • _____ Repair: Visible light photolyase

Genetic Recombination

Crossing over

_____ _____: Exchange of genes between two DNA molecules

_____ _____: Two chromosomes break apart and rejoin

• Insertion of foreign DNA into chromosome

• RecA Protein

Transformation

Conjugation

Transduction

Types of Horizontal Gene Transfer

_____: Genes transferred from one bacterium to another as “naked” DNA

_____: Plasmids transferred from one bacterium to another

Requires cell to cell contact - sex pili

_____: DNA transferred from a donor cell to a recipient cell via bacteriophage (or phage)

• Generalized or Specialized

Generalized

Specialized

_____ Transduction: Random DNA packaged into the phage and transferred

_____ Transduction: Specific bacterial genes are packaged inside the phage and transferred

Plasmids

Self-replicating circular pieces of DNA

• 1-5% size of bacterial chromosome

• Often code for proteins that enhance the pathogenicity of a bacterium

• Conjugative or Dissimilation, Resistance Factors

Exist independently of chromosomal DNA

Conjugative

Dissimilation

Resistance

_____ Plasmids: Carries genes for sex pili and transfer of plasmid

_____ Plasmids: Encode enzymes for the catabolism of unusual compounds

_____ Factors: Encode antibiotic resistance

Transposons

Small segments of DNA (Chromosomes or plasmids)

• Can move from one region of DNA to another

• Contain insertion sequences (IS) - code for transposase

  • Cuts and reseals DNA and may carry additional genes for resistance or pathogenicity.

• Complex transposons carry other genes

Biotechnology

Use of microorganisms, cells, or cell components to make a product (Food, antibiotics, vitamins, enzymes)

Recombinant

_____ Technology: Insertion or modification of genes to produce desired proteins

Vector

Self-replicating DNA molecule

• Transport foreign DNA into cell

• Ex. Plasmids and viruses

Clone

Population of genetically identical cells arising from one cell

Restriction

_____ Enzyme: Cut specific nucleotide sequences from DNA

Polymerase

_____ Chain Reaction: Process that amplifies DNA for analysis

Used for;

• Identifying microbes that can’t be cultured

• Detecting pathogens

• Diagnostic tests for genetic diseases

doubles

In each PCR cycle, the amount of DNA _____

DNA Ligase

An enzyme that makes covalent bonds between the sugar of one nucleotide and the phosphate groups in another nucleotide in DNA is…?

RNA Polymerase

Responsible for building RNA from a DNA template during transcription.

DNA Helicase

Unzips the DNA double helix by breaking hydrogen bonds between base pairs

DNA Polymerase

Adds new nucleotides to a growing DNA strand during replication & forms the covalent bonds (phosphodiester bonds) between them

Is essential for proofreading and error correction.

Use codons to determine polypeptide sequences

Protein synthesis in eukaryotes is similar to the process in prokaryotes in that both eukaryotes and prokaryotes…?

Photolyase

Thymine dimers can be repaired by light-repair enzymes known as…?

Conjugation

The process for gene transfer which requires cell-to-cell contact and a particular type of plasmid is called…?

Conjugation

Transduction

Crossing over

Transformation

_____ - a type of horizontal gene transfer in bacteria that:

• Requires direct cell-to-cell contact.

• Involves a conjugative plasmid (like the F plasmid in E. coli).

• DNA is transferred through a pilus from a donor to a recipient cell.

_____ - Gene transfer mediated by a bacteriophage (virus), not direct contact.

_____ _____ - Occurs during meiosis in eukaryotes, not in bacterial gene transfer.

_____ - Involves uptake of free DNA from the environment, no contact required.

Transposons

The small segments of DNA that can move from one region of a DNA molecule to another

Operons

In bacteria, operons are groups of genes regulated together. Control gene expression.

Transposition

The process where a specific DNA segment, called a transposon, moves from one location in a genome to another, either within the same DNA molecule or between different DNA molecules