Microbiology a human perspective

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1

Genome

The complete set of genetic information of a cell

2

Gene

The functional unit of the genome

3

Genomics

Study of the nucleotides sequence of DNA

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DNA

Double strand , helical structure, each strand has a chain of deoxyribonucleotide(nucleotides)

5

Nucleotide

Each nucleotides contains 5 carbons sugar ( deoxyribose), a phosphate group and one of the four nucleobases(A,T,G OR C)

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DNA replication

The double strand of dna must be duplicated before cell division

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Gene expression

The information encoded by DNA Must be decoded so that the cell can synthesis the necessary gene product

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2 events of gene expression

Transcription and translation

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Transcription

The information encoded in DNA is copied into a slightly different molecule

can initiate without promoter

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Translation

The information carried by RNA is interpreted to synthesis the encoded protein

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The central dogma

The flow of information from DNA to RNA to protein

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Sugar phosphate backbone

The joining of nucleotides to create a series of alternative sugar and phosphate units

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DNA complementary

Held together by hydrogen bonds between nucleobases

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RNA

Single strand

Has Ribose

15

Difference between DNA and RNA

RNA has Ribose not deoxyribose in dna

RNA has an oxygen molecule not dna

RNA contains uracil not thymine in dna

single strand linear shorter than dna

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3 functional types of RNA

Messenger RNA

ribosal RNA

transfer RNa

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M RNA

Type of RNA molecule translated during protein synthesis

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T RNA

Type of rna molecule involves in interpreting the genetic code, each tRNA carries a specific amino acids

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Ribosomes

Facilitate the joining of amino acid during translation, contain rRNA and protein

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Origin of replication

When the replication process is bidirectional it proceed from a specific starting point

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DNA replication process

DNA is replicated so that each of the two cell generate during binary fission , it s generally bidirectional and proceeds from a specific amino acid called origin of replication. The progression of bidirectional replication around a circular dna create two advancing forks where dna synthesis is occurring.these regions are called replication forks it meets terminating sites where the process is complete

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Semi conservative

The original strand conserved paired with the the newly synthesis strand

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The proteins that bind to the origin of replication

DNA gyrase and helicases temporarily break and unwind the DNA helix at that site

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Enzyme Primase

Synthesize small fragments of RNA to serve as primers for dna synthesis

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Primer

Fragment of nucleic acid in which DNA polymerase can add nucleotides

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DNA ligase

Joins two dna fragments together by forming convanlent bond

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Replisome

The complex of enzymes and other protein that synthesis DNA

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Okazaki fragments

Nucleic acid fragments produced during discontinuous synthesis of the lagging strand

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DNA polymerase

Use of strand of dna as a template to make the complementary strand

add nucleotides to the 3’end

synthesis occurs in 5’ to 3’ direction

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Helicase

Unzips the two strands of DNA

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Leading strand

3’ending

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Lagging strand

5’ending, DNA polymerase cannot add nucleotides, synthesis must be reinitiated

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How long it takes E. coli to replicate

40 minutes

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Promoter

Nucleotide sequence to which rna polymerase bind to initiate transcription

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Minus strand

Strand that dna serve as the template for rna synthesis

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Plus strand

Strand of dna complementary to the one that serve as the template for Rna it has uracil rather than thymine

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RNA polymerase

Enzymes that synthesize RNA using single strand DNA as template 5’to 3’direction

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Sigma factor

Component of RNA polymerase that recognizes the promoter region

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Terminator

Nucleotide sequence at which rna synthesis stop

Rna polymerase falls off the dna template and release the newly synthesized dna

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Monocistronic

A transcript that carries one gene

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Elongation of the RNA transcrip

RNA polymerase move along dna using the minus strand as a template to synthesis a single strand RNA molecule

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Initiation

RNA polymerase bind to the promoter and melt a short stretch of Dna

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Role of Ribosome

They serve as a translation machine structure that string amino acids together to make a polypeptide

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Promoter

Orientate direction of the transcription

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Redundancy

One amino acid is coded for by more than one codon

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Ribosome

Maintain correct reading frame

align and form peptides bond between amino acid

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Translation in prokaryotes

Begin before transcription is complete-polyribosome

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Ribosome has 2 sites in which tRNA can bind to

P site occupy by tRNA

another tRna occupy a A site , bring the correct amino acid

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Elongation of polypeptide chain

Ribosome adnvance along mRNA in 5’ to 3’

initiate Trna exits to E site

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Post translation modification

Polypeptide often modify after synthesis

some must be folded into specific three dimensional structure with help of protein chaperone

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 Microorganisms constantly face changing environment

• Alternating periods of feast and famine
• Host eats, bacteria take up amino acids, vitamins, nutrients

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Signal transmission

• Transmits information from outside cell to inside • Allows cells to monitor and react

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Quorum Sensing

• Some organisms can “sense” density of their population

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Phase variation

• involves switching genes on and off

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Antigenic variation

• is alteration of characteristics of surface proteins

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Constitutive enzymes

synthesize constantly

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Inductive enzyme

Not routinely produced

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Repressible enzymes

Produce routinely

Turned off when not required

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Induction

Repressor bind and blocks transcription

transcription is usually off

repressor unable to bind / transcription on

60

The lac Operon as a Model

it uses a repressor that prevent transcription when lactose is not available but when lactose is available some is converted to allolactose