Ch 10: Nature, Ch 10: Nature, structure and structure and organisation of organisation of genetic materialgenetic material

Nature of Genes-Analysing Nature of Genes-Analysing DNADNA

Genes made of deoxyribonucleic acid (DNA). DNA made of building blocks called Genes made of deoxyribonucleic acid (DNA). DNA made of building blocks called nucleotides.nucleotides.

Form a chain=4 diff types of nucleotides.Form a chain=4 diff types of nucleotides. Adenine-ThymineAdenine-Thymine Cytosine-GuanineCytosine-Guanine

Each nucleotide has a sugar (deoxyribose) part, phosphate part and a Nitrogen base.Each nucleotide has a sugar (deoxyribose) part, phosphate part and a Nitrogen base. Sugar & phosphate always same in all 4 nucleotides.Sugar & phosphate always same in all 4 nucleotides. Bases differ A, T, C, G.Bases differ A, T, C, G.

DNADNA When nucleotides join to form a When nucleotides join to form a

chain, bonds form between the chain, bonds form between the sugar of 1 nucleotide and sugar of 1 nucleotide and phosphate group of the next phosphate group of the next nucleotide.nucleotide.

1 chain of nucleotides run from 1 chain of nucleotides run from head to tailhead to tail Phosphate is head end (5’ prime Phosphate is head end (5’ prime

end)end) Sugar is tail end (3’ prime end)Sugar is tail end (3’ prime end)

A-T and C-G are in equal A-T and C-G are in equal proportion in the body. Known proportion in the body. Known as Chargaff’s rule.as Chargaff’s rule.

DNA forms a double helixDNA forms a double helix Nucleotide chain organised into Nucleotide chain organised into

double helix shape. double helix shape. Each chain runs in opposite Each chain runs in opposite

direction and are anti-parallel.direction and are anti-parallel. Sugar phosphate backbone of the Sugar phosphate backbone of the

2 chains are on the outside of 2 chains are on the outside of helix-coil around.helix-coil around.

Bases arranged to point inwards.Bases arranged to point inwards. Bases in 1 chain pair with bases Bases in 1 chain pair with bases

on the 2on the 2ndnd chain. A-T, C-G are chain. A-T, C-G are held together by hydrogen bonds held together by hydrogen bonds between the base pairs-between the base pairs-complementary.complementary.

DNADNA DNA:DNA: Can act as a template for Can act as a template for

its own replication.its own replication. Contain genetic Contain genetic

instructionsinstructions Can undergo change or Can undergo change or

mutationmutation Base sequence could be Base sequence could be

GGTACGTA. Its GGTACGTA. Its complementary chain is complementary chain is CCATGCATCCATGCAT

DNA partnersDNA partners DNA strand can be separated DNA strand can be separated

into 2 single strands- into 2 single strands- DissociationDissociation..

Done through heating at 90*- Done through heating at 90*- breaks strong sugar-phosphate breaks strong sugar-phosphate bond that join nucleotides in 1 bond that join nucleotides in 1 chain.chain.

Forms 2 single chains of DNAForms 2 single chains of DNA If cools, hydrogen bonds reform If cools, hydrogen bonds reform

and DNA becomes double helix and DNA becomes double helix again: Re-association.again: Re-association.

Pairing between Pairing between complementary DNA chains or complementary DNA chains or parts of chains from different parts of chains from different sources-sources-hybridisationhybridisation..

DNA to chromosomes and DNA to chromosomes and genes.genes.

Longer chromosome, more DNA it has and more genes it carries.Longer chromosome, more DNA it has and more genes it carries. Length of double-strand DNA determined by no. of base pairs Length of double-strand DNA determined by no. of base pairs

(bp). Single strand is no. of bases (b). (bp). Single strand is no. of bases (b). DNA in a haploid cell 3000 million bp (1m). DNA divided among DNA in a haploid cell 3000 million bp (1m). DNA divided among

23 chromosomes (4 cm) has about 120 million bp.23 chromosomes (4 cm) has about 120 million bp.

Mitochondria DNAMitochondria DNA Generate and store energy in Generate and store energy in

ATP form (eukaryote cells).ATP form (eukaryote cells). Have DNA and mtDNA is Have DNA and mtDNA is

double stranded circular double stranded circular molecule.molecule.

Have 16568 bp & 37 genesHave 16568 bp & 37 genes 13 code for proteins involved in 13 code for proteins involved in

cellular respirationcellular respiration 2 genes code for ribosomal DNA 2 genes code for ribosomal DNA

(rRNA)(rRNA) 22 genes code for transfer RNA 22 genes code for transfer RNA

(tRNA)(tRNA) Circular mtDNA has 37 genes. Circular mtDNA has 37 genes.

1 part (D-loop) doesn’t contain 1 part (D-loop) doesn’t contain genes. Why? Becomes genes. Why? Becomes displaced during replication.displaced during replication.

Gene sequencingGene sequencing ATGGTGCA etc… is part of a ATGGTGCA etc… is part of a

nucleotide sequence of the HBB nucleotide sequence of the HBB gene which controls production of gene which controls production of haemoglobin.haemoglobin.

Gene sequencing involves the Gene sequencing involves the process of identifying the process of identifying the nucleotides along a gene.nucleotides along a gene.

DNA bands are produced-tell you DNA bands are produced-tell you what nucleotide and the order of what nucleotide and the order of the bands tells you gene sequence.the bands tells you gene sequence.

Used on all org. except retrovirus Used on all org. except retrovirus because have RNA.because have RNA.

Different genetic instructions within Different genetic instructions within & between species are due to & between species are due to different nucleotides sequences in different nucleotides sequences in the genes.the genes.

Nature of the genetic Nature of the genetic codecode

Genetic code in DNA Genetic code in DNA contains info from joining contains info from joining amino acids to form amino acids to form proteins.proteins.

Coded InfoCoded Info Nucleotide seq. in DNANucleotide seq. in DNA

Decoded InfoDecoded Info Order of amino acids in Order of amino acids in

proteinsproteins

Organisation of genetic codeOrganisation of genetic code DNA sequence can be DNA sequence can be

separated into 3 bases-called separated into 3 bases-called triplet code or codon. triplet code or codon.

TAC,AAA,CAA,GCT,CCTTAC,AAA,CAA,GCT,CCT Produces amino acid:Produces amino acid: met, phe, val, arg, gly amino met, phe, val, arg, gly amino

acids produced.acids produced. Amino acid can be produced Amino acid can be produced

by more than 1 triplet code.by more than 1 triplet code. Amino Acid produced can be a Amino Acid produced can be a

STOP instruction or START STOP instruction or START instruction.instruction.

What is a GenomeWhat is a Genome The genome is the total set of The genome is the total set of

genes carried by an individual or genes carried by an individual or cell.cell.

About 20000-25000 total.About 20000-25000 total. Mainly inside the nucleus or Mainly inside the nucleus or

eukaryotic cells.eukaryotic cells. Genomes of individuals usually Genomes of individuals usually

differ in a single base of the differ in a single base of the DNA sequence. Known as DNA sequence. Known as Single nucleotide Single nucleotide polymorphisms (SNP’s)polymorphisms (SNP’s)

Are similarities between 2 Are similarities between 2 unrelated individuals. 99.9% unrelated individuals. 99.9% same but over 3 million same but over 3 million differences!differences!

Human Genome ProjectHuman Genome Project Aims to completely analyse Aims to completely analyse

the genome sequence of the genome sequence of humans.humans.

2 human genomes are 2 human genomes are sequenced & by comparing 2 sequenced & by comparing 2 sets of data, generalisations sets of data, generalisations can be made. can be made. Help provide info and diagnose Help provide info and diagnose

genetic diseasesgenetic diseases ID factors that cause diseases-ID factors that cause diseases-

help preventhelp prevent Understand how genes act and Understand how genes act and

how they cause disease-how they cause disease-treatmenttreatment

Understand genetic control of Understand genetic control of human development.human development.

Proteomics: study of proteins made by the genome.

MutationsMutations Genetic material can change-Genetic material can change-

Mutations.Mutations. Genes can appear suddenly or Genes can appear suddenly or

change in the genome-Mutationchange in the genome-Mutation A mutation is a change in an A mutation is a change in an

allele due to a change in DNA.allele due to a change in DNA. Is an alteration/Change in the Is an alteration/Change in the

genome.genome. Spontaneous mutationSpontaneous mutation: when : when

causative agent cant be causative agent cant be identifiedidentified

Induced MutationInduced Mutation: When : When causative agent can be found.causative agent can be found.

Mutagenic agentsMutagenic agents: Agents that : Agents that cause mutation (x-rays, cause mutation (x-rays, ulltraviolet/nucelar radiation, ulltraviolet/nucelar radiation, chemical substances.chemical substances.

Kinds of MutationsKinds of MutationsOriginal:Original:

AAT GTC GGA GTCAAT GTC GGA GTC10 20 0010 20 00

SubstitutionSubstitution: Replace 1 nucleotide with : Replace 1 nucleotide with anotheranother

AAT AAT CCTC GGA GTCTC GGA GTC10 20 0010 20 00

Replaced G with C at no.13Replaced G with C at no.13 AdditionAddition: Insert 1 or more nucleotides : Insert 1 or more nucleotides

into DNA strandinto DNA strandAAT GTC GGAAT GTC GGTT AGT C AGT C

10 20 00 10 20 00

Adding a T between original nucleotides Adding a T between original nucleotides (17-18)(17-18)

DeletionDeletion: removal of 1 or more : removal of 1 or more nucleotides from DNA strandnucleotides from DNA strand

AAT GAAT GCGCG GAG TC GAG TC10 2010 20

Deleted T between G and C from original Deleted T between G and C from original (no 13-15)(no 13-15)

Effects?Effects? Sometimes no effect: Change Sometimes no effect: Change

from GGA to GAG still codes for from GGA to GAG still codes for same amino acid leusame amino acid leu-Silent -Silent mutationmutation

Sometimes cause major Sometimes cause major change: Change from ACA to change: Change from ACA to ACT makes diff. amino acid ACT makes diff. amino acid (cys) which is a STOP.(cys) which is a STOP.

Single base mutations Single base mutations (deletions) have a big effect (deletions) have a big effect because affect certaiin triplet because affect certaiin triplet but all others that follow- but all others that follow- Frameshift mutationFrameshift mutation..

Trinucleotide repeat Trinucleotide repeat mutationsmutations

Some triplets codes are Some triplets codes are repeated in genome.repeated in genome.

Trinucleotide repeat expansion Trinucleotide repeat expansion (TRE)(TRE) mutations involves mutations involves additional repeats of these additional repeats of these triplets and leads to disease.triplets and leads to disease.

Normal allele has smaller no. of Normal allele has smaller no. of nucleotide repeats whereas a nucleotide repeats whereas a mutant allele has a longer one mutant allele has a longer one because of all the repeats.because of all the repeats.

Mutation is unstable-repeats Mutation is unstable-repeats can change from 1 generation can change from 1 generation to the next. to the next. E.g. HD mutated allele increases E.g. HD mutated allele increases

its repeats from father to kids.its repeats from father to kids.

Does it matter?Does it matter? Somatic mutationSomatic mutation: mutation : mutation

occurs in body cell (muscle, occurs in body cell (muscle, brain etc…). Only that cell and brain etc…). Only that cell and daughter cell made by mitosis daughter cell made by mitosis will have mutation. will have mutation.

Not passed onto next Not passed onto next generation. generation.

Germline mutationGermline mutation: Mutation in : Mutation in cell that produces gametes. cell that produces gametes.

Are heritable because gamete Are heritable because gamete with mutation can give rise to with mutation can give rise to offspring. offspring.

DNA repairDNA repair DNA can repair itself but is DNA can repair itself but is

limited.limited. Best way stop DNA Best way stop DNA

damage from UV radiation-damage from UV radiation-protection. protection.

Sunblock, hats, sunscreen.Sunblock, hats, sunscreen. Can cause skin cancerCan cause skin cancer DNA damaging radiation in DNA damaging radiation in

sunlight is UV-B. Increased sunlight is UV-B. Increased exposure due to ozone exposure due to ozone hole.hole.