Molecular Basis of HeredityMolecular Basis of Heredity

DNADNA

Instructions are Instructions are inherited inherited (passed) from (passed) from parent to offspring in the form of a parent to offspring in the form of a geneticgenetic codecode known as known as genesgenes

DNADNA: Molecules that carry the genetic code.: Molecules that carry the genetic code.

The code is The code is used to make used to make PROTEINSPROTEINS

The The proteinsproteins become cell parts and become cell parts and carry outcarry out most most functionsfunctions of the cell. of the cell.

DNA MoleculeDNA Molecule

Genes are made up of molecules of DNA:Genes are made up of molecules of DNA: “ “DDeoxyriboeoxyribonnucleic ucleic aacid”cid”Found in nucleus.Found in nucleus.Controls manufacture of enzymes, proteinsControls manufacture of enzymes, proteinsMade up of repeating subunits known as Made up of repeating subunits known as

nucleotide subunitsnucleotide subunits..

The nucleotide is made of 3 “parts”The nucleotide is made of 3 “parts”1. Phosphate group1. Phosphate group2.2. A sugar, called “deoxyribose”A sugar, called “deoxyribose”3.3. Nitrogenous base (the “rungs of the ladder”)Nitrogenous base (the “rungs of the ladder”)

} (“sides” of the ladder)

The double helixThe double helix

Nucleotides - DNANucleotides - DNA

Nitrogenous Nitrogenous base: base: Adenine “A” (always pairs with “T”)Adenine “A” (always pairs with “T”)Thymine “T” (always pairs with “A”)Thymine “T” (always pairs with “A”)Guanine “G” (always pairs with “C”)Guanine “G” (always pairs with “C”)Cytosine “C” (always pairs with “G”)Cytosine “C” (always pairs with “G”)Forms the “rung” of the ladderForms the “rung” of the ladder

DNA ReplicationDNA ReplicationDuring reproduction DNA makes During reproduction DNA makes exact copiesexact copies of itself of itself

called called REPLICATION. REPLICATION. Occurs in nucleus during both Occurs in nucleus during both mitosis and meiosis.mitosis and meiosis.DNA polymerase (an enzyme!) causes the two DNA polymerase (an enzyme!) causes the two

strands (sides) to “unzip”: the bonds between the strands (sides) to “unzip”: the bonds between the base pairs breakbase pairs break

TEMPLATETEMPLATE: Each side serves as a pattern or : Each side serves as a pattern or template. Each base pair will attract the template. Each base pair will attract the complementary nucleotidecomplementary nucleotide A—T or G—C A—T or G—C

The two DNA strands will be identicalThe two DNA strands will be identical

Genetic CodeGenetic CodeGenetic Code: Heredity informationGenetic Code: Heredity information--depends upon the order of the nucleotides --depends upon the order of the nucleotides

in the DNA molecule.in the DNA molecule.--determines --determines which typewhich type of protein is made of protein is madeGene:Gene: the sequence of nucleotides that the sequence of nucleotides that

make the protein make the protein Triplet codes:Triplet codes: group of three nucleotides that group of three nucleotides that

is specific to each amino acid.is specific to each amino acid.also known as a CODONalso known as a CODON

RNA and Protein SynthesisRNA and Protein Synthesis

DNA provides the instruction to make proteinsDNA provides the instruction to make proteins

But . . . DNA is too large to pass through the nuclear But . . . DNA is too large to pass through the nuclear membrane (double strand too BIG) How will it get the membrane (double strand too BIG) How will it get the instructions out of the nucleus?instructions out of the nucleus?

RNA!RNA!RNA exists as a RNA exists as a single strand single strand which is small enough to pass which is small enough to pass through nuclear membranethrough nuclear membrane

Messenger “mRNA” is made in the Messenger “mRNA” is made in the nucleusnucleusThey serve as “messengers” from DNA to They serve as “messengers” from DNA to the ribosome. the ribosome. RNA base pairing: RNA base pairing: Cytosine—Guanine C—G AdenineCytosine—Guanine C—G Adenine—Uracil A—U —Uracil A—U (not T!!)(not T!!)

Really important!!

RNA- RNA- RRiboibonnucleic ucleic aacidcidDNADNA RNARNA

Sugar: deoxyriboseSugar: deoxyribose Sugar: riboseSugar: ribose

Nitrogen bases: adenine, Nitrogen bases: adenine, thymine, cytosine, thymine, cytosine, guanineguanine

Nitrogen bases: adenine, Nitrogen bases: adenine, cytosine, guanine and cytosine, guanine and uracil instead of thymineuracil instead of thymine

Double-strandedDouble-stranded Single-strandedSingle-stranded

Only one kind of DNAOnly one kind of DNA Three kinds:Three kinds:messenger RNA (messenger RNA (mmRNARNA), ), ribosomal RNA (ribosomal RNA (rrRNARNA),),transfer RNA (transfer RNA (ttRNARNA))

Ribosomal RNA makes up the major Ribosomal RNA makes up the major portion of the Ribosome (the site of protein portion of the Ribosome (the site of protein synthesis) Location: cytoplasm!synthesis) Location: cytoplasm!Transfer RNA Transfer RNA transfers amino acids transfers amino acids to the to the ribosome during protein synthesisribosome during protein synthesis

Protein Synthesis Protein Synthesis

DNA DNA mmRNA ProteinRNA Proteintranscription translation

(nucleus) (cytoplasm)

The The order of the basesorder of the bases in the DNA specifies in the DNA specifies the the order of bases order of bases in the in the mRNAmRNA, and , and

The The order of basesorder of bases in the in the mRNAmRNA specifies specifies the the order of amino acidsorder of amino acids in a protein. in a protein.

TranscriptionTranscription

RNA polymerase (an enzyme!) binds to the DNA RNA polymerase (an enzyme!) binds to the DNA and separates the DNA strandsand separates the DNA strandsOne strand of the DNA acts as a One strand of the DNA acts as a templatetemplate from from which nucleotides are assembled into a strand of which nucleotides are assembled into a strand of mRNA.mRNA.This strand is complementary to the DNA, This strand is complementary to the DNA, except that except that uraciluracil binds to adeninebinds to adenine not thymine! not thymine!

(BTW, what happens to the other strand of DNA?)(BTW, what happens to the other strand of DNA?)

Protein SynthesisProtein Synthesis

REMEMBER: The RNA is only single REMEMBER: The RNA is only single stranded!stranded!The mRNA may now pass through the The mRNA may now pass through the nuclear membrane into the cell and over to nuclear membrane into the cell and over to the the ribosomeribosome

TranslationTranslation

During During translationtranslation, the , the mRNAmRNA transported transported to the cytoplasm is "de-coded" or to the cytoplasm is "de-coded" or "translated" to produce the correct order of "translated" to produce the correct order of amino acids in a protein amino acids in a protein Nucleotides on Nucleotides on mRNAmRNA are read " are read "three at three at a timea time" (3= codon) by the ribosome" (3= codon) by the ribosomeThe mRNAThe mRNA will bind with will bind with ttRNA at the RNA at the codons codons

TranslationTranslationtRNAtRNA = transfer RNA; small RNA molecules that = transfer RNA; small RNA molecules that carry a carry a specific amino acidspecific amino acid at one end and an at one end and an anticodonanticodon region that recognizes and binds to region that recognizes and binds to the the codoncodon ( (mRNA)mRNA) at the other end. The at the other end. The tRNA.tRNA.The The codoncodon of the mRNA determines what amino of the mRNA determines what amino acid is added to a protein chain.acid is added to a protein chain.The process continues, chaining the amino acids The process continues, chaining the amino acids together until the “stop” codon is reached together until the “stop” codon is reached

Codon – anti codonCodon – anti codonLysine

codon

Anti-codon

Methionine

Changing Chromosome StructureChanging Chromosome Structure

TranslocationTranslocation: transfer of one section of a : transfer of one section of a chromosomechromosomeAdditionAddition: a portion of one chromosome is : a portion of one chromosome is attached to another chromosome attached to another chromosome DeletionDeletion: a portion of a chromosome is taken : a portion of a chromosome is taken away from a chromosome away from a chromosome InversionInversion: a portion of a chromosome breaks off : a portion of a chromosome breaks off and then becomes reattached to the same and then becomes reattached to the same chromosome in an inverted (upside down) chromosome in an inverted (upside down) fashion fashion