BSc. Genetics

7/30/2019 BSc. Genetics

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Genetics

Study of Genes03 / 05/2012


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On completion of this moduleyou must

Define Bacterial Genetics

Understand terms used in Bacterial

Genetics Describe the structure of DNA

Describe Gene Expression in Bacteria

Describe transcription in Bacteria

Describe Translation in Bacteria ( OutlineProtein synthesis steps


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On completion of this moduleyou must

Understand Mutations

Describe the bacterial Genetic Transfer:

Conjugation

Transformation

Transduction


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What is Genetics?

The manipulation of DNA to study cellular

and organismal function

DNA encodes all of the information tomake the cell and the complete organism


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Introduction

Single Circular DNA Material

DNA of the smallest free-living organismhas a molecular weight of 5 x 108

Bacteria are haploid

The DNA of human cells contain about 3x 109 base pairs and can code about 1000

000 proteins


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Introduction

DNA consists of 2 strands wrapped

around each other I a double helix

Each strand consists of a chain of

nucleotides held together by phosphates

joining their deoxyribose sugar


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Structure of DNA

Strands(chains):Deoxyribonucleotides

A base

A sugar

A phosphate group


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DNA BasesAdenine (A)

Cytosine( C)

Thymine (T)

Guanine


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DNA BasesBases with two rings:

A and G (PURINES

Bases with one ring:

T and C ( PYRIMIDINES)


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DNA BasesA third pyrimidine, uracil (U), replaces

thymine in RNA

All four DNA bases are attached to the

five-carbon sugar deoxyribose

The sugar is identical to ribose , which is

found in RNA except it does not have an

oxygen attached to the second carbon


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The DNA chain

Phosphodiester bonds join

deoxynucleotide link in the DNA chain


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Introduction

DNA is synthesized from the precusor

deoxynucleoside triphosphates by DNApolymerase

The DNA in a bacterium that carriesmost of the genes is called the bacterial

chromosome


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Mutations

A mutation is a change in the base

sequence of DNA that usually results ininsertion of a different amino acid into

a protein and the appearance of an

altred phenotype


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Mutations

A mutation is any heritable change in thesequence of DNA of an organism.

The organism with a mutation is called a

mutant, and that organism's mutant

phenotype includes all the characteristics

that are different from the wild-type, ornormal organism


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Base substitution

A mutation in which one type of basepair in DNA ( e.g. an AT pair) is changed

into a different base pair

( e.g. GC pair )


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Missense mutations

A base pair change mutation in a regionof DNA encoding a polypeptide that

changes an amino acid in the polypeptide

This occurs when a base substitutionresults in a codon that simply causes a

different amino acid to be inserted


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Nonsense codons

Usually the codons UAG, UGA and UAA.

These codons do not stipulate an amino

acid in most types of organisms but,

rather, trigger the termination of

tranlation


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Nonsense mutations

In a region of DNA encoding a protein, a

base pair change mutation that causes

one of the nonsense codons to be

encountered in frame when mRNa is

translated


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Frame shift mutation

Any mutation that adds or removes one

or more ( but not a multiple ) base

pairs from DNA , whether or not it

occurs in the coding region for a

protein


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Causes of Mutations

Chemical

Radiation

Viruses


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Chemical Mutations

Some chemicals such as 5-bromouracil,

are base analogues- the resemble normal

bases

Bromine has an atomic radius similar to

that of methyl- group

Therefore 5-bromouracil can be iserted in

place of thymine


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Chemical Mutations

Some chemicals, such as benzpyrene,

found in tobacco smoke, bind to the

existing DNA bases and cause frame

mutations

These chemicals are often carcinogenic


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Transfer of DNA within bacterialcell

Transposon:

A DNA sequence that can move from one

place in DNA to a different place with the

help of transposase enzymes


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This can be done by a promiscous

plasmids:

This is a self-transfmissible plasmid

that can transfer itself into many types

of bacteria, some of which are onlydistantly related to each other

Transfer of DNA within bacterial


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Programmed Rearrangements: These may be silent genes that encode

variants of the antigens and the

insertion of a new gene into the activesite in a sequential, repeated

programmed manner.

These are not induced by an immune

response but have the effect of

allowing organisms to evade it


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Conjugation

The transfer of DNA from one bacterial

cell to another by the transfer functions

of a self-transmissible DNA element such

as a plasmid


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Conjugation

Self-transmissible plasmids can

transfer themselves to other bacterilacells

Mobilizable plasmids cannot transferthemselves but can be transferred by

certain self-transmissible plasmids


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Conjugation

The process by which self-transmissible

plasmids promote their own transfer or

the transfer of other plasmids into cells is

called conjugation

The original cell that contained theplasmid is the donor, and the cell into

which the plasmid has been tranferred

are called transconjugants


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Conjugation

Bacterial strains with a self-transmissible

plasmid inserted into their chromosome

are called Hfr strains


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Conjugation

Self-transmissible plasmids have several trans-

acting Tra genes that encode products requiredfor transfer, as well as a cis-acting oriT site at

which plasmid transfer originates


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Transformation

Bacteria that are capable of taking up

DNA are said to be competent

Some types of bacteria can naturally take

up DNA during part of their life cycle

In transformation, DNA is taken directly

by cells


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Transformation

Most types of naturally transformable

usually become competent only duringpart of their cellular growth, when they

have reached high densities and are

entering the stationary phase


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Transformation

Some types of bacteria, including

Haemophilus infleunzaeand Neisseriagonorrhoea, will take up DNA of only

the same species


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Transduction

A process in which DNA other than

phage DNA is introduced into thebacterium is introduced into bacterium

by infection by a phage containing DNA


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Processes leading to proteinsynthesis

Transcription:

Is the synthesis of RNA on a DNA

template

This process is probably fairly similar in

all organisms, but it is best understood in

bacteria

RNA is a polymer made up of a chain of

ribonucleotides


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Processes leading to proteinsynthesis

The bases of the nucleotides:

Adenine, cytosine, uracil, and guanine

The enzyme responsible for making RNA

is called RNA polymerase


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Translation

This is the process by which the region of

mRNA encodes a protein

BSc. Genetics

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