(MMI) Lecture 8 (Chapter 8 and 9)

Role of Genetic Material

• Store information for the biochemical and structural components of the cell

• Replicate to pass the information to the next generation

• Generate genetic variation to provide diversity in the population

What does the genome do?

The genome determines all the organism inherited traits and defines the species of the organism.

Functions of DNA include…

1. Self-replication

2. Genetic material of all organisms

3. Genetic material of some virus

Genetics

The study of what genes are, how they carry information, how information is expressed, and how genes are replicated and propagated.

Gene

A segment of DNA that encodes for a protein.

Genotype

All of the genes present in an organism.

Phenotype

Physical characteristics of the organism based upon the expression of their genes.

Genome

All of the genetic material in a cell (coding & non-coding).

Genomics

The molecular study of genomes.

DNA replication

DNA is copied by DNA polymerase, always in the 5' 3' direction, initiated by an RNA primer.

Leading strand

Synthesized continuously during DNA replication.

Lagging strand

Synthesized discontinuously (stop-start) in small pieces known as Okazaki fragments.

Okazaki fragments

Small pieces of DNA synthesized on the lagging strand during DNA replication.

Transcription

The process by which mRNA is made from a DNA template by RNA polymerase.

RNA polymerase

The enzyme that binds to the promoter sequence to initiate transcription.

mRNA (messenger RNA)

Carries genetic instructions out of the nucleus to a ribosomes, where instructions are used to build proteins.

Translation

The process of converting the info stored in the RNA into proteins. The codons will specify which amino acid needs to be inserted into the growing polypeptide/protein.

Codons

Groups of three nucleotides in mRNA that are translated into amino acids.

Start codon

The codon AUG at which translation of mRNA begins.

Stop codon

Codons UAA, UAG, UGA at which translation ends.

Degenerate code

The description of the genetic code where several codons encode the same amino acid.

Eukaryotes

Organisms whose mRNA requires additional processing to remove introns.

Coupled transcription and translation

transcription and translation can be coupled together because they lack a nuclear membrane

Constitutively expressed genes

Genes which produce protein all the time at a fixed rate.

Repressible genes

Genes that are turned on by default and switched off when not needed

Inducible genes

Genes that are expressed only as needed and can be turned on. (Switched on when needed)

Operon (Bacterial gene organization)

Genes encoding the enzyme components of a metabolic pathway are often organized together into an operon.

Lac operon

A specific example of inducible gene expression where a repressor protein prevents transcription of lactose metabolism genes.

Repressor protein in lac operon

Always made and sticks to the promoter region preventing transcription of the genes needed for lactose metabolism.

Lactose effect on lac operon

If lactose is present, it binds to and inactivates the repressor allowing transcription of the lactose metabolism genes.

Repressible gene expression

A type of gene expression regulation where the presence of a specific molecule inhibits gene expression.

Tryptophan biosynthesis operon

A cluster of genes involved in the synthesis of tryptophan that is regulated by the availability of tryptophan.

What are the three principical mechanism of which bacteria reproduce asexually?

1. Transformation

2. Conjugation

3. Transduction

Transformation

The process by which DNA released from dead bacteria is taken up by living bacteria and integrated into their genome.

Conjugation

The process of transferring genetic material between bacterial cells through direct contact, typically involving a plasmid and a sex pilus.

What does bacterial conjugation involve?

The copying and passing of a plasmid from (F+) ot a recipient (F-)

Transduction

The transfer of genes between cells by viruses. Can either happen through the lytic cycle or lysogenic cycle.

Lytic cycle (Transduction)

1. The phage will attach and inject DNA

2. Phage DNA will circularize

3. New P.DNA synthesized and assembled into virions

4. Cell lyses , releasing virions

Lysogenic cycle (Transduction)

1. The phage will attach and inject DNA

2. Phage DNA will circularize

3. P.DNA integrates with bacterial chromosome=prophage

4. Lysogenic bacterium reproduces normally (CELL DIVISION)

Mutation

Any change in the normal sequence of nucleotides in a piece of DNA.

Missense mutation

A mutation that results in the substitution of one amino acid for another in a protein.

Nonsense mutation

A mutation that converts a codon into a stop codon, leading to premature termination of protein synthesis.

Frame-shift mutation

A mutation caused by the insertion or deletion of nucleotides that alters the reading frame of the gene.

Deletion

A genetic change where one or more nucleotides or a larger segment of a chromosome is lost during DNA replication

Insertion

A genetic change where one or more extra nucleotide base pairs are added into a DNA sequence

Spontaneous mutation rate

The frequency at which mutations occur naturally in an organism.

Mutagens

Agents that increase the mutation rate.

Examples of mutagens

Ultraviolet light, radiation, and some chemicals that can increase mutation rates.

Conjugative plasmids

Plasmids that contain genes encoding the pilus necessary for bacterial conjugation.

Antibiotic resistance genes

Genes often found on plasmids that confer resistance to antibiotics.

Virus excision

The process by which a virus removes itself from a host genome, which can sometimes include bacterial DNA.

Genetic recombination

The process by which genetic material is exchanged between organisms, leading to genetic diversity.

Asexual reproduction in bacteria

A method of reproduction where bacteria replicate without the fusion of gametes, leading to genetic variation through recombination.

Griffith's experimental proof

An experiment demonstrating the process of transformation in bacteria. Found that he could kill mice when injecting with the dead cells of a virulent streptococcus pneumoniae.

Bacterial chromosome

The circular DNA molecule that contains the genetic information of a bacterium.

Next generations (what are they?)

Subsequent offspring that inherit genetic material from their predecessors.

The Flow of Genetic Information

1. Expression

2. Recombination

3. Replication

Expression

Genetic information is used within a cell to produce the proteins needed for the cell to function

Recombination

Genetic information can be transferred between cells of the same generation.

Replication

Genetic information can be transferred between generations of cells. (Daughter cells)

The functions of RNA include…

1. Protein Synthesis

2. Genetic material of some viruses

3. Comprises viroids

What is DNA replication?

The biological process where a cell makes an identical copy of its DNA before cell division.

DNA Helicase

Unwinds double-stranded DNA

DNA gyrase

Remove the supercoils as DNA strands unwinds ahead of the replication fork and transcription machinery

DNA Polymerase III

Polymerizes nucleotides to synthesize DNA; DNA proofreading

DNA polymerase I

Removes RNA primers and replaces them with nucleotides

DNA ligase

Links Okazaki fragments together

What do bacterial genomes look like?

Their genome is contained in a circular chromosome

DNA replication in many bacteria occurs bi-directionally (2 replication forks), why is it that this is possible?

The unique circular shape of bacterial DNA

• the origin site (oriC) contains DnaA boxes that force the two DNA strands to apart.

• Can simultaneously copy and divide.

When does transcription begin and when does it end?

Begins when RNA polymerase binds to the promoter sequence and ends when it reaches the terminator sequence,

What do bacterial genes lack and why?

They lack introns for fast replication

Transfer RNA (tRNA)

A structural link which contains anti-codons to match the codon and amino acid that the mRNA is coding for.

Ribosomal RNA (rRNA)

Structural components of ribosomes, is the small subunit and large subunit and holds everything together.

MicroRNA (miRNA)

Various regulatory functions, causes mRNA degradation or stops ribosomes from making proteins.