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Part 2 - Molecular Microbial Genetics - Coggle Diagram
Part 2 - Molecular Microbial Genetics
DNA replication
Steps
1)
Helicase unwinds parental double helix
2)
Single strand binding proteins stabilize unwound parental DNA
3)
Leading strand synthesized continuously in 5’ —> 3’ direction by DNA polymerase
4)
Lagging strand synthesized discontinuously, primase
Leading
:
Primase
(adds primer, short sequence of RNA, signals starting point).
DNA Polymerase
(makes new DNA strand using original as template).
DNA made continuously.
Lagging
:
Primase
(adds primer, short sequence of RNA, signals starting point).
DNA Polymerase
(makes new DNA strand using original as template).
DNA made in fragments
(Okazaki).
DNA Ligase
(seals gaps between fragments)
Origin of replication
Specific DNA sequence where DNA replication is initiated, marking the starting point for DNA duplication
P:
single origin of replication per chromosome (cytoplasm).
E
: multiple origins to facilitate replication of larger genomes (nucleus)
Essential for accurate DNA duplication & transfer of genetic information to daughter cells
Adenine and thymine require 2 hydrogen bonds (easier to melt/separate strain). Cytosine and guanine require 3
Single-strand binding protein (SSB): Protein binds to strains after helicase, keeps them separated, without, strain will coil back.
Mutation
Base substitution/point mutation:
Missense
(substitutoin of different a.a,
Sickle Cell Anemia
).
Nonsense
(base substitution, stop codon in middle of mRNA)
Framsshift
: 1+ nucleotide pairs deletered/inserted in DNA, results in shift of translationional reading frame and inactive protein production,
Huntington's disease
Spontaneous
: absense of mutation causing agent, errors in DNA replication.
Mutagens
: Agents that cause mutation.
Chemical, radiation, UV light
Silent
: base code changes, but a.a is the same,
CUU mutates to CUG = no change in protein
. Can be harmful and removed when cell dies, can be beneficial and introduce new trail to enhance survival.
Mutation rate
: % that gene will mutate when cell divides. Small, negative exponents.
Spontanous rate
is 10^-6.
Mutagens
increase rate from 10^-1000x to 10^-3 - 10^-5
Genetic recombination
Exchange of genes between 2 DNA molecules, new gene combinations
Crossing over occurs in
E
cells, Prophase 1 of meiosis. P cells must use
Gene transfer
Verticle
: Genes passed from organism to offspring.
Horizontal
: Bacteria increase diversity.
Transformation
(Acquisition of DNA from environment).
Transduction
(Involves a virus).
Conjugation
(2 different strains of bacteria, donor and recipient)
Transformation
: 2 cells closelt related, only small pieces of DNA taken, cells that can take in donor DNA are "competent." Occurs naturally in few bacteria:
Gram (+)
bacillus, streptococcus, staphylococcus.
Gram (-)
haemophilus, neisseria, acrinetobacter.
Conjucation
: Mediated by "fertility plasmid."
Donor
(F+ or Hfr).
Recipient
(F-).
Result
(2 F+ cells)
Plasmids
: Extra chromosome that can be found in some bacteria.
Sorted by function
-
Conjugation
: Codes for sex pili (bridge for DNA exchange).
Dissimilation
: Codes of enzymes that trigger catabolism of unusual substrates.
R Factors
: Makes host cell resistant to antibiotics, inactivate certain drugs.
Pathogenicity
: Codes for toxin production
Transduction
: Bacterial DNA transferred from donor cell to recipient inside virus (bacteriophage). Specialized: DNA is transferred inside lysogenic virus
Transposons
: DNA can move from one region to another. Chromosome to chromosome, chromosome to plasmid. Can cause mutation
Protein Synthesis
Decodes mRNA to produce polypeptide. Polypeptide formed when amino group of 1 amino acid forms amide bond with carboxyl group of another amino acid. Reaction is catalyzed by ribosomes
On mRNA, sequences of 3 nucleotides is called a
codon
. 64 possible codons to code for 20 amino acids. 3 stop codons
Gene Expression
Instructions on DNA transcribed onto mRNA
Ribosomes able to read genetic info inscribed on strand of mRNA
They use info to string amino acids into proteins
DNA > RNA > Proteins - Link between genotype and phenotype. Gene
: Allel that codes for color of eyes.
Phenotype*: Color of eyes
Why protein?
Only macromolecule with many diverse functions (structural & mechanical, enzymes, hormones, antibodies, fluid balance, acid-base balance, channels & pumps, transport)
Operon Model
How transcription is regulated
Operator
: Stop/go for transcription.
Promotor
: RNA polymerase binding site on DNA.
Structural gene
: Determines proteins produces
Repression Model
Transcription shut down based on enzyme produced. Response to overabundance of end product, mediated by repressors
Inducible Operon
Stops in absence of substrate. Active repressor protein binds to operator, preventing transcription of structural genes
Transcription & Translation
In bacteria, mRNA is synthesizes in cytoplasm, so translation and
transcription can occur simultaneously
Translation
1 -
Initiation
(mRNA attaches to smaller subunit of ribosome, AUG start codon, a tRNA w/ appropriate anticodon attaches, larger subunit of ribosome comes in). 2 -
Elongation
(tRNAs move in w/ appropriate amino acid, a.a. chain grows using peptidyl transferase).
Termination
(Stop codon is reached, amino acid chain is processed.
E
= a.a. chain moved into endoplasmic reticulum)
Transcription
Occurs in one strain of DNA (RNA polymerase synthesizes in 5' to 3' direction, unwinds and rewinds DNA as read. Elongation occurs at 40 nucleotides / second
Upstream of gene
: anything before gene of interest (transcription initiation site).
Downstream of gene
: everything past gene of interest (transcription termination site)
1 -
Initiation
(promotor is a piece of DNA upstream, indicates where RNA polymerase should bind). 2 -
Elongation
(RNA polymerase adds complimentary nucleotides, A, U, C, G). 3 -
Termination
(RNA cleaved and released)