MicrobialGenetics

UNIT 02:MICROBES ANDHEALTHLife scienceRamesh Kumar

Image: Prokaryotic Replication, U.S.National Library of MedicineFrom the Virtual Microbiology Classroom on ScienceProfOnline.com

UNIT 02:MICROBES ANDHEALTHLife scienceRamesh Kumar

Genetics

• Genetics deals with the molecularstructure and function of genes, genebehavior, patterns of inheritance fromparent to offspring, and gene distribution,variation and change in populations.

• Genetics deals with the molecularstructure and function of genes, genebehavior, patterns of inheritance fromparent to offspring, and gene distribution,variation and change in populations.

Nucleic Acid

• Nucleic acids are biological molecules essentialfor life

• Nucleic acids allow organisms to transfer geneticinformation from one generation to the next.

• There are two types of nucleic acids:– Deoxyribonucleic acid, better known as DNA– Ribonucleic acid, or RNA.

• Nucleic acids are biological molecules essentialfor life

• Nucleic acids allow organisms to transfer geneticinformation from one generation to the next.

• There are two types of nucleic acids:– Deoxyribonucleic acid, better known as DNA– Ribonucleic acid, or RNA.

What is DNA ???

• DNA is a double stranded structure like atwisted ladder. It is embedded in the nucleus ofeukaryotic cell but in prokaryotic it is lying incytoplasm because of the absence of nucleus.

• Discovered by Oswald Avery in 1944 with ateam of scientists.

• The nucleus of one human cell containsapproximately 2 meter of DNA.

• DNA is a double stranded structure like atwisted ladder. It is embedded in the nucleus ofeukaryotic cell but in prokaryotic it is lying incytoplasm because of the absence of nucleus.

• Discovered by Oswald Avery in 1944 with ateam of scientists.

• The nucleus of one human cell containsapproximately 2 meter of DNA.

DNA (cont….)

• The basic structural units of DNA arenucleotides.– Nucleotides form a gene– Genes form DNA– DNA forms chromosome

• Nucleotides are complex structures composed ofthree kinds of molecules as1. Nitrogenous Base2. Deoxyribose sugar3. Phosphate group

• The basic structural units of DNA arenucleotides.– Nucleotides form a gene– Genes form DNA– DNA forms chromosome

• Nucleotides are complex structures composed ofthree kinds of molecules as1. Nitrogenous Base2. Deoxyribose sugar3. Phosphate group

Nitrogen Base:• In DNA the nitrogen bases are

1. Adinine (A),2. Thymine (T),3. Guanine (G)4. Cytocine (C)

• The information in DNA is stored as a codemade up of these four bases.

• In DNA the nitrogen bases are1. Adinine (A),2. Thymine (T),3. Guanine (G)4. Cytocine (C)

• The information in DNA is stored as a codemade up of these four bases.

Deoxyribose sugar Phosphate group• Deoxyribose sugar and Phosphate groups

arrange alternatively and act as a backbone ofDNA.

• The deoxyribose sugar of one nucleotide isattached to the phosphate group of the nextnucleotide.

• Deoxyribose sugar and Phosphate groupsarrange alternatively and act as a backbone ofDNA.

• The deoxyribose sugar of one nucleotide isattached to the phosphate group of the nextnucleotide.

What is RNA???

• RNA is the second principal kind of nucleic acid.

• It is a single stranded structure.

• It has ribose sugar (C5 H10 O5) having one moreoxygen atom than deoxyribose sugar (C5 H10 O4)in DNA

• The nitrogen base in RNA contains Uracil insteadof Thymine.

• RNA is the second principal kind of nucleic acid.

• It is a single stranded structure.

• It has ribose sugar (C5 H10 O5) having one moreoxygen atom than deoxyribose sugar (C5 H10 O4)in DNA

• The nitrogen base in RNA contains Uracil insteadof Thymine.

RNA (cont….)

• In RNA, thymine (T) is replaced by Uracil(U) and the rest of them are the same.

• In RNA the nitrogen bases are1. Adinine (A)2. Uracil (U)3. Guanine (G)4. Cytocine (C)

• In RNA, thymine (T) is replaced by Uracil(U) and the rest of them are the same.

• In RNA the nitrogen bases are1. Adinine (A)2. Uracil (U)3. Guanine (G)4. Cytocine (C)

RNA Structure

Types of RNA

RNA is of three types as:

– Messenger RNA (mRNA),

– Transfer RNA (tRNA)

– Ribosomal RNA (rRNA)

RNA is of three types as:

– Messenger RNA (mRNA),

– Transfer RNA (tRNA)

– Ribosomal RNA (rRNA)

Types of RNA (cont…)

• mRNA: messenger RNA acts as a template forprotein synthesis

• tRNA: It brings amino acids to the ribosomal sitewhere they are incorporated into proteins

• rRNA: It forms ribosome and is its integral part.

• mRNA: messenger RNA acts as a template forprotein synthesis

• tRNA: It brings amino acids to the ribosomal sitewhere they are incorporated into proteins

• rRNA: It forms ribosome and is its integral part.

Difference in DNA & RNA

DNA RNA

Has Deoxyribose sugar Has Ribose sugar

Double stranded Single strandedDouble stranded Single stranded

Nitrogen bases are A,G, T and C Are A, G, C and U

Has one type Three types as mRNA, rRNA andtRNA

Transfers hereditarycharacteristics

Synthesizes protein

Function of DNA• DNA) is the genetic code which ensures that daughter cells inherit the

same characteristics as the parent cells

• DNA is the code from which all protein is synthesized

• DNA also contains all the genetic coding which is used to controlfunctions

• DNA is also used as a long term storage device to store the geneticinstructions

• genetic coding which is used to control behaviour and development

• DNA) is the genetic code which ensures that daughter cells inherit thesame characteristics as the parent cells

• DNA is the code from which all protein is synthesized

• DNA also contains all the genetic coding which is used to controlfunctions

• DNA is also used as a long term storage device to store the geneticinstructions

• genetic coding which is used to control behaviour and development

Function of RNAo mRNA carries instructions on how to connect several "amino acids"

o tRNA is the actual translator

• Sequence of amino acids is put together

o mRNA carries instructions on how to connect several "amino acids"

o tRNA is the actual translator

• Sequence of amino acids is put together

MutationMutation

Mutation

• A change in the nucleotide sequence ofa gene (< 1%), polymorphism (>1%)

• May occur at the molecular orchromosomal level

• The effect of mutations vary• Mutant refers to an unusual phenotype• Mutations are important to evolution

• A change in the nucleotide sequence ofa gene (< 1%), polymorphism (>1%)

• May occur at the molecular orchromosomal level

• The effect of mutations vary• Mutant refers to an unusual phenotype• Mutations are important to evolution

Mutations

• Change in the DNA

• May occur spontaneously or by exposureto a radiation or chemicals

• An agent that causes a mutation is amutagen

• Change in the DNA

• May occur spontaneously or by exposureto a radiation or chemicals

• An agent that causes a mutation is amutagen

Spontaneous Mutation

• De novo or new mutations• Not caused by exposure to known

mutagen• Errors in DNA replication• DNA bases have slight chemical instability• Exist in alternating forms called tautomers• As replication fork encounters unstable

tautomers, mispairing can occur

• De novo or new mutations• Not caused by exposure to known

mutagen• Errors in DNA replication• DNA bases have slight chemical instability• Exist in alternating forms called tautomers• As replication fork encounters unstable

tautomers, mispairing can occur

Spontaneous Mutation

Spontaneous Mutation Rate• Rate differs for different genes

– Vary by size– Sequence dependence– Hot spots– Table 12.3 lists rates for several genes

• On average, 1/100,000 each round ofreplication

• Each individual has multiple newmutations

• Most by are not in coding regions of genes

• Rate differs for different genes– Vary by size– Sequence dependence– Hot spots– Table 12.3 lists rates for several genes

• On average, 1/100,000 each round ofreplication

• Each individual has multiple newmutations

• Most by are not in coding regions of genes

Induced Mutations• Caused by mutagens, many are also carcinogens and

cause cancerExamples:• Alkylating agents: remove a base• Acridine dyes: add or remove base• Xrays: break chromosomes

delete a few nucleotides• UV radiation: creates thymidine dimers

• Site-directed mutagenesis:

• Caused by mutagens, many are also carcinogens andcause cancer

Examples:• Alkylating agents: remove a base• Acridine dyes: add or remove base• Xrays: break chromosomes

delete a few nucleotides• UV radiation: creates thymidine dimers

• Site-directed mutagenesis:

Exposure to Mutagens

• Workplace• Industrial accidents

– Chernobyl• Medical treatments• Weapons• Natural sources

• Workplace• Industrial accidents

– Chernobyl• Medical treatments• Weapons• Natural sources

Point MutationsA change of a single nucleotide• Transition

purine replaces purineA to G or G to A or

pyrimidine replaces pyrimidineC to T or T to C

• Transversionpurine replaces pyrimidine orpyrimidine replaces purine

A or G to T or C T or C to A or G

A change of a single nucleotide• Transition

purine replaces purineA to G or G to A or

pyrimidine replaces pyrimidineC to T or T to C

• Transversionpurine replaces pyrimidine orpyrimidine replaces purine

A or G to T or C T or C to A or G

Missense Mutation

• A point mutation that changes the codon• Causes a substitution of an amino acid• Missense mutations may affect protein

function severely, mildly, or not at all.

Example:• Hemoglobin mutation• Glutamic acid to valine causes sickle cell

anemia

• A point mutation that changes the codon• Causes a substitution of an amino acid• Missense mutations may affect protein

function severely, mildly, or not at all.

Example:• Hemoglobin mutation• Glutamic acid to valine causes sickle cell

anemia

Nonsense Mutation• A point mutation changing a codon for an

amino acid into a stop codon• Creates truncated proteins that are often

nonfunctional• Some have dominant effects due to

interference with normal functionsExample:• A factor XI deficiency is a nonsense

mutation changing glutamic acid to a“stop”

• Short protein cannot function in clotting

• A point mutation changing a codon for anamino acid into a stop codon

• Creates truncated proteins that are oftennonfunctional

• Some have dominant effects due tointerference with normal functions

Example:• A factor XI deficiency is a nonsense

mutation changing glutamic acid to a“stop”

• Short protein cannot function in clotting

Insertions or Deletions• The genetic code is read in triplet

nucleotides• Addition or subtraction of nucleotides not

in multiples of three leads to a change inthe reading frame

• Causes a frameshift and alters aminoacids after mutation

• Addition or subtraction of nucleotides inmultiples of three leads to addition orsubtraction of entire amino acids

• The genetic code is read in tripletnucleotides

• Addition or subtraction of nucleotides notin multiples of three leads to a change inthe reading frame

• Causes a frameshift and alters aminoacids after mutation

• Addition or subtraction of nucleotides inmultiples of three leads to addition orsubtraction of entire amino acids

Gene Transfer Mechanisms –Conjugation (cont.)Transformation and

Transduction

• ConjugativeTransposons

• These genetic elementsshare attributes withconjugal plasmids andtransposons

• A transposition eventbetween two cells

• Requires all thefunctions found inconjugation plus thoseof transposition

• ConjugativeTransposons

• These genetic elementsshare attributes withconjugal plasmids andtransposons

• A transposition eventbetween two cells

• Requires all thefunctions found inconjugation plus thoseof transposition

Transformation• Tranformation is process of taking up

naked DNA in a stably inherited form.• Two major types of transformation1. Natural transformation (only a subset of

microbes do this)• - usually linear DNA• 2. Artificially-induced (most, but not all

microbes can be induced to take up DNA• - usually plasmid DNA• A cell that is proficient to take up DNA is

described as competent

• Tranformation is process of taking upnaked DNA in a stably inherited form.

• Two major types of transformation1. Natural transformation (only a subset of

microbes do this)• - usually linear DNA• 2. Artificially-induced (most, but not all

microbes can be induced to take up DNA• - usually plasmid DNA• A cell that is proficient to take up DNA is

described as competent

Transduction• Genetic exchange mediated by bacterial viruses

(bacteriophage)

• Two basic types of bacterial viruses

• Lytic viruses – infect cells, multiply rapidly, lyse cells

• Lysogenic viruses – infect cells, can integrate intogenome and go dormant (a prophage)

• - at some point, can excise, multiply and lyse cells

• Genetic exchange mediated by bacterial viruses(bacteriophage)

• Two basic types of bacterial viruses

• Lytic viruses – infect cells, multiply rapidly, lyse cells

• Lysogenic viruses – infect cells, can integrate intogenome and go dormant (a prophage)

• - at some point, can excise, multiply and lyse cells

• Bacteriophage have a range ofmorphologies from simple filaments tolarge complex structures

• May contain either RNA or DNAassociated with a protein coat

• Almost all bacteria have phage associatedwith them

• Bacteriophage have a range ofmorphologies from simple filaments tolarge complex structures

• May contain either RNA or DNAassociated with a protein coat

• Almost all bacteria have phage associatedwith them

Attach to specific receptors on the surface oftheir host bacteria

Transfer their nucleic acid into the host cell

Lysogeny of bacteriophage

Integrate into host genome - Enter a semi-dormant state

(eg. Lambda phage)

METABOLISM

OF

PROTEINS

METABOLISM

OF

PROTEINS

DIGESTION AND ABSORPTION OFPROTEIN

NITROGEN BALANCEAmount of nitrogen taken in food = Amount of nitrogen

excreted/day

• POSITIVE NITROGEN BALANCEAmount of nitrogen taken in food > Amount of nitrogen

excreted/day• NEGATIVE NITROGEN BALANCEAmount of nitrogen taken in food < Amount of nitrogen

excreted/day

Amount of nitrogen taken in food = Amount of nitrogenexcreted/day

• POSITIVE NITROGEN BALANCEAmount of nitrogen taken in food > Amount of nitrogen

excreted/day• NEGATIVE NITROGEN BALANCEAmount of nitrogen taken in food < Amount of nitrogen

excreted/day

TRANSAMINATION &DEAMINATION

TRANSAMINATION:Transamination is a reaction in which one or more aminoacids are converted into other amino acid. The reaction iscatalyzed by transaminases or aminotransferases.

DEAMINATION:A catabolic reaction in which amino group is removedforming an keto acid & ammonia. The reaction is catalyzedby amino acid oxidase.

CH3-CH-COOH amino acid oxidase CH3-C-COOH + NH3

NH2 OAlanine Pyruvic acid (keto acid)

TRANSAMINATION:Transamination is a reaction in which one or more aminoacids are converted into other amino acid. The reaction iscatalyzed by transaminases or aminotransferases.

DEAMINATION:A catabolic reaction in which amino group is removedforming an keto acid & ammonia. The reaction is catalyzedby amino acid oxidase.

CH3-CH-COOH amino acid oxidase CH3-C-COOH + NH3

NH2 OAlanine Pyruvic acid (keto acid)

• The transamination reaction results in the exchangeof an amine group on one acid with a ketone group onanother acid.

DECARBOXYLATIONDecarboxylation is a reaction in which carboxylgroup of an amino acid is removed & convertsinto an amine group.

HR-C-COOH amino acid dehydrolase R-CH2-NH2 + CO2

NH2 pyridoxal phosphate

Example: Decarboxylation of histidine to formhistamine

Decarboxylation is a reaction in which carboxylgroup of an amino acid is removed & convertsinto an amine group.

HR-C-COOH amino acid dehydrolase R-CH2-NH2 + CO2

NH2 pyridoxal phosphate

Example: Decarboxylation of histidine to formhistamine

UREA CYCLE

CENTRAL DOGMA

Crick's central dogma: Information flow is from DNAto RNA via the process of transcription, and thenceto protein via translation.

Crick's central dogma: Information flow is from DNAto RNA via the process of transcription, and thenceto protein via translation.