Microbiology Chapter 11: Mechanisms of Microbial Genetics

Gene

• A sequence of DNA that encodes a functional product

• Normally proteins

Semiconservative

• Process classification

• Used in DNA replication

- One stand of the parental DNA is used in the new daughter cell while one new strand is synthesize

DNA Gyrase

• Enzyme used in DNA replication process

• Relaxes the supercoiled DNA

Helicase

• Enzyme used in DNA replication process

• Separates the strands of DNA

- Named because it unwinds the helix

DNA polymerase III

• Enzyme used in DNA replication process

• Main polymerase that adds new nucleotides

Primase

• Enzyme used in DNA replication process

• Lays down RNA primer on the lagging strand

- Contains a (3’OH) group that DNA polymerase can replicated DNA from

DNA polymerase I

• Enzyme used in DNA replication process

• Replaces the RNA primer in Okazaki Fragments with DNA

Ligase

• Enzyme used in DNA replication process

• Ligates Okazaki fragments together

- Sticks Okazaki fragments together

• Ligates DNA strands that have been snipped by enzyme Topoisomrase IV

Topoisomerase IV

• Enzyme used in DNA replication process

• Nicks one daughter strand to allow for separation

Ligates

• To join together

Single Strand Binding Protein

• Important protein that is used in the DNA replication process

• Binds to the single helix DNA to make it more stable

- In more stable form its replicated

Lagging Strand

• One of two stands of DNA formed after the DNA helix is unraveled

• Runs in 3 to 5 direction

• Replicated discontinuously by the enzymes Primase and DNA polymerase III

Replication of Circular Chromosome

• Used in bacteria

• Bi-directional replication

- About 1,000 nucleotides per second

• One origin of replication

• Topoisomerase IV separates daughter cells

Replication of Linear Chromosome

• Used in Eukaryotes

• Multiple origins of replication

- About 100 nucleotides a second

• Slightly different enzymes involved

RNA Polymerase

• Enzyme used in the beginning stages of transcription

• Opens up the DNA where it binds

- Facilitated by σ factor

Template Stand

• The strand of DNA that the mRNA is made off of

• Runs in the 3 to 5 direction

Coding Stand

• The strand of DNA that is not being used to make mRNA

• Matches the mRNA sequence

- U in mRNA are T in DNA

• Runs in the 5 to 3 direction

Termination Sequence

• The last subsection of a gene

• The codon that allows the ribosomes to disassociate from the gene

Eukaryotic mRNA Modification

• Needed because mRNA needs to travel from the nucleus to the ribosomes elsewhere in the cell

• Methyl cap

• polyA tail

• Coated with stabilizing proteins

Codon and Amino Acid Relationship

• Multiple codons code for the same amino acid

Ribosoms

• Made of proteins and rRNA

• Has subunits

- Large subunit 50s, binds to mRNA second

- Small subunit 30s, binds to mRNA first

tRNA

• Delivers amino acids to peptide chain

• Shaped like a clover leaf

- One end has an anticodon

- The other end has an amino acid that is specified by the anticodon

Ribosome Binding Site

• Part of the mRNA that allows the ribosome to recognize it

AUG

• Start codon

Initiation

• First step in making a polypeptide chain

• Ribosomes bind to mRNA

- Forming transitional process

• tRNA brings the first amino acid in to start the polypeptide chain

Elongation

• Second step in making a polypeptide chain

• Ribosome moves down the mRNA strand codon by codon

• tRNA brings an amino acid per codon and adds it to the polypeptide chain

Termination

• Last step in making a polypeptide chain

• Ribosome hits the stop codon

• Transitional complex disassociates from the mRNA and the polypeptide chain is relaeased

Transitional Complex

• A structure formed when the two ribosomal subunits combine together with the mRNA sequence

Leading Strand

• One of two stands of DNA formed after the DNA helix is unraveled

• Runs in 5 to 3 direction

• Replicated continually by the enzyme DNA polymerase III

Okazaki Fragments

• A fragment of DNA, 1000 base pairs

• Made from a lagging strand

• Combined together by the enzyme ligase

Promoter Region

• The beginning subsection of a gene

• Very attractive to RNA Polymerase

Coding Region

• The second subsection of a gene

• The part that is actually made into mRNA