Genetic CodeGenetic Code&&

MutationsMutations

Exons and IntronsExons and Introns

EXONSEXONS A segment of DNA A segment of DNA

in eukaryotic in eukaryotic organisms that organisms that codes for a specific codes for a specific amino acidamino acid

INTRONSINTRONS A segment of DNA A segment of DNA

that does NOT that does NOT code for an amino code for an amino acid.acid.

Confusing genetic terms:Confusing genetic terms:

PolypeptidePolypeptide = a chain of amino = a chain of amino acids.acids.

ProteinProtein = a complex structure = a complex structure composed composed of polypeptides of polypeptides

Amino acidsAmino acids = smallest structural = smallest structural unit of a unit of a polypeptide. polypeptide.

GeneGene = a distinct unit of material = a distinct unit of material found on found on a chromosomea chromosome

““Language of RNA”Language of RNA”RNA contains 4 different bases: A,U,C,GRNA contains 4 different bases: A,U,C,GThe genetic code is responsible for The genetic code is responsible for

building all the proteins in the body building all the proteins in the body using using 20 different amino acids20 different amino acids..

CodonCodon: three consecutive nucleotides : three consecutive nucleotides that specify a single amino acid.that specify a single amino acid.Amino acids are attached to make a Amino acids are attached to make a

polypeptide, polypeptide, proteinprotein..AnticodonAnticodon: the complimentary RNA : the complimentary RNA

bases of a codon.bases of a codon.

CodonsCodons

A three letter “word” that A three letter “word” that specifies an amino acid.specifies an amino acid.

There are “start” codons & “stop” codonsThere are “start” codons & “stop” codonsTells ribosome where to start reading the Tells ribosome where to start reading the

RNA strand.RNA strand.

Genetic code:Genetic code:

TranslationTranslation TRANSLATIONTRANSLATION: : the process by which mRNA is the process by which mRNA is

read and protein produced.read and protein produced. mRNA has a codon that codes for a particular mRNA has a codon that codes for a particular

anticodon, attached to tRNA (translational RNA)anticodon, attached to tRNA (translational RNA) tRNA also has the amino acid attached to it.tRNA also has the amino acid attached to it.

tRNA (transfer)tRNA (transfer)

approx. 80 approx. 80 nucleotides in nucleotides in length.length.

Cross-like shapeCross-like shape At one end there is At one end there is

an anticodonan anticodon At other end an At other end an

amino acid is amino acid is attachedattached

MutationsMutations

MutationMutation is a change in genetic is a change in genetic material.material.

Types of Mutations:Types of Mutations:Gene MutationsGene Mutations

A. Point MutationA. Point Mutation

B. Frameshift MutationB. Frameshift MutationChromosomal MutationsChromosomal Mutations

Gene MutationsGene Mutations

Point MutationPoint Mutation: occur at a single point: occur at a single pointIncludes substitution, addition, and Includes substitution, addition, and

deletions of bases.deletions of bases.May only change one amino acid coded for.May only change one amino acid coded for.

Frameshift MutationFrameshift Mutation: when codons get : when codons get changed because of additions or changed because of additions or deletionsdeletionsChanges the combinations so that different Changes the combinations so that different

amino acids are coded for.amino acids are coded for.

Chromosomal MutationsChromosomal Mutations

These mutations change the entire These mutations change the entire chromosome.chromosome.

Types include:Types include:DeletionsDeletions: loses part of chromosome: loses part of chromosomeDuplicationsDuplications: doubles part of : doubles part of

chromosomechromosomeInversionsInversions: inverts part of chromosome: inverts part of chromosomeTranslocationsTranslocations: takes part of : takes part of

chromosome and moves it to other part chromosome and moves it to other part of chromosomeof chromosome

Translocation

Insertion

A six-legged green frog

A white American alligator shows a genetic mutation

known as leucism. This allele controls migration of pigment

cells during development; absence in cells leads to white

patches on the skin

An African clawed frog (Xenopus laevis), mutated, with three hind legs

Control of gene expressionControl of gene expression

Genes are often like light Genes are often like light switches that can be turned off switches that can be turned off and on.and on.

OperonOperon = occur in prokaryotes. = occur in prokaryotes. (bacteria) different genes that (bacteria) different genes that work together to activate gene work together to activate gene functionsfunctions

Eukaryotic gene expressionEukaryotic gene expression

Controlled Controlled by complex by complex sequences sequences of DNA. of DNA.

Example: Example: ““TATA boxTATA box””

Hox and OncogenesHox and Oncogenes

Hox genesHox genesGenes that Genes that

actively actively control control embryonic embryonic development.development.

OncogenesOncogenesGenes known to Genes known to

cause cancer.cause cancer.Usually these Usually these

are switched are switched “off”, but can be “off”, but can be switched “on” by switched “on” by a number of a number of factors.factors.