Chapter 10: DNA and Chapter 10: DNA and RNARNA

DNADNA

Deoxyribonucleic acidDeoxyribonucleic acidStructure of DNAStructure of DNA Made up of four subunits Made up of four subunits

called called nucleotidesnucleotidesEach nucleotide is made up Each nucleotide is made up of a sugar, a phosphate and of a sugar, a phosphate and a basea base

Four BasesFour Bases

Two PurinesTwo Purines Adenine (A)Adenine (A) Guanine (G)Guanine (G)

Two pyrimidinesTwo pyrimidines Cytosine (C)Cytosine (C) Thymine (T)Thymine (T)

DNA Double HelixDNA Double Helix

DNA is made of two nucleotide strands DNA is made of two nucleotide strands that wrap around each other in the that wrap around each other in the shape of a double helix.shape of a double helix.

DNA StructureDNA Structure

Bonds Hold DNA TogetherBonds Hold DNA Together Nucleotides along each DNA strand are linked Nucleotides along each DNA strand are linked

by covalent bonds. by covalent bonds. Complementary nitrogenous bases are Complementary nitrogenous bases are

bonded by bonded by hydrogen bonds.hydrogen bonds.

ChargaffChargaffAmount of adenine Amount of adenine equals the amount equals the amount of thymine and the of thymine and the amount of cytosine amount of cytosine equals the amount equals the amount of guanineof guanineA=TA=TC=GC=G

But what does DNA look But what does DNA look like?like?

Rosalind FranklinRosalind Franklin Working in Wilkin’s lab Working in Wilkin’s lab

created x-ray pictures of DNAcreated x-ray pictures of DNA Wilkins shared this Wilkins shared this

information with another pair information with another pair of scientists without Franklin’s of scientists without Franklin’s consentconsent

Watson and CrickWatson and Crick

Watson and Crick Watson and Crick discovered that discovered that DNA resembles a DNA resembles a twisted ladder twisted ladder shape: shape: double double helixhelix

DNA StructureDNA Structure

Two side of the ladder are made Two side of the ladder are made up of alternating sugar and up of alternating sugar and phosphate moleculesphosphate moleculesThe rungs of the ladder are pairs The rungs of the ladder are pairs of bases (A with T, and G with C): of bases (A with T, and G with C): Base pair ruleBase pair ruleRungs are anti-parallel (5’->3’ and Rungs are anti-parallel (5’->3’ and 3’ ->5’)3’ ->5’)

Making copies: ReplicationMaking copies: Replication

DNA can “unzip” DNA can “unzip” when it needs to when it needs to replicate (helicase)replicate (helicase)Occurs prior to cell Occurs prior to cell division so each division so each new cell gets the new cell gets the correct informationcorrect information

ReplicationReplicationDNA molecule separates into two DNA molecule separates into two strandsstrandsComplementary strands form on the Complementary strands form on the template of each of the original sides template of each of the original sides of the DNAof the DNAEach new DNA has one old and one Each new DNA has one old and one new strand (semiconservative new strand (semiconservative replication)replication)

Replication enzymesReplication enzymes

HelicaseHelicase Unwinds DNAUnwinds DNA

PrimasePrimase Adds an RNA primer on unzipped DNAAdds an RNA primer on unzipped DNA

DNA polymeraseDNA polymerase Add new bases to the 3’ end of previous baseAdd new bases to the 3’ end of previous base

LigaseLigase Seals fragments after RNA primer removedSeals fragments after RNA primer removed

Steps of DNA ReplicationSteps of DNA Replication

Replication begins with the separation of Replication begins with the separation of the DNA strands by the DNA strands by helicaseshelicases. .

Then, Then, primaseprimase adds an RNA primer adds an RNA primer where replication will occurwhere replication will occur

DNA polymerasesDNA polymerases form new strands by form new strands by adding complementary nucleotides to adding complementary nucleotides to each of the original strands.each of the original strands.

The new segments of DNA are sealed The new segments of DNA are sealed by by ligaseligase

http://www.dnareplication.info/images/dnareplication.jpg

http://www.johnkyrk.com/DNAreplication.html

See it in action:

DNA ReplicationDNA Replication

DNA ReplicationDNA Replication

Each new DNA Each new DNA molecule is made molecule is made of one strand of of one strand of nucleotides from nucleotides from the original DNA the original DNA molecule and one molecule and one new strand. This is new strand. This is called called semi-semi-conservative conservative replicationreplication..

Replication Forks Increase the Speed Replication Forks Increase the Speed of Replicationof Replication

ReplicationReplication

DNA polymerase can only add to a 3’ endDNA polymerase can only add to a 3’ end

Leading strand Leading strand Runs 5’->3’Runs 5’->3’

Lagging strandLagging strand Runs 3’->5’ SO can’t add directlyRuns 3’->5’ SO can’t add directly Have to replicate in fragments called Okazaki Have to replicate in fragments called Okazaki

fragmentsfragments Ligase bonds the fragments togetherLigase bonds the fragments together

DNA ReplicationDNA Replication

OverviewOrigin of replication

Leading strand

Leading strand

Lagging strand

Lagging strandOverall directions

of replication

Leading strand

Lagging strand

Helicase

Parental DNA

DNA pol III

Primer Primase

DNA ligase

DNA polymerase

DNA polymerase

Single-strand binding protein

5

3

5

5

5

5

3

3

3

313 2

4

Replication animationReplication animation

http://www.mcb.harvard.edu/Losick/imagehttp://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swfs/TromboneFINALd.swf

Central DogmaCentral Dogma

Has its exceptions, but gives us a basic Has its exceptions, but gives us a basic idea of how DNA does its jobidea of how DNA does its job

RNARNA

Single stranded nucleic acidSingle stranded nucleic acid

Made up of nucleotidesMade up of nucleotides

Sugar: RiboseSugar: Ribose

Thymine instead of UracilThymine instead of Uracil

Shorter: length of one geneShorter: length of one gene

RNA Structure and Function RNA Structure and Function Types of RNATypes of RNA Cells have three major Cells have three major

types of RNA: types of RNA:

messenger RNAmessenger RNA (mRNA)(mRNA)

ribosomal RNA (rRNA)ribosomal RNA (rRNA)

transfer RNA (tRNA)transfer RNA (tRNA)

ActivityActivity

In pairs, create a chart that will fit in your In pairs, create a chart that will fit in your foldable (no more than 1/8th size of foldable (no more than 1/8th size of construction paper) that compares and construction paper) that compares and contrasts the different forms of RNAcontrasts the different forms of RNABe sure to include:Be sure to include: NameName StructureStructure FunctionFunction PicturePicture

RNA Structure and FunctionRNA Structure and Function

mRNAmRNA carries the genetic “message” carries the genetic “message” from the nucleus to the cytosol.from the nucleus to the cytosol.

rRNArRNA is the major component of is the major component of ribosomes.ribosomes.

tRNA tRNA carries specific amino acids, carries specific amino acids, helping to form polypeptides.helping to form polypeptides.

Making proteinsMaking proteins

Cells use a two step process to Cells use a two step process to read each gene and produce the read each gene and produce the amino acid chain that becomes a amino acid chain that becomes a protein.protein.These processes are:These processes are: TranscriptionTranscription TranslationTranslation

http://gslc.genetics.utah.edu/units/basics/transcribe/

Fig. 17-4Fig. 17-4

DNAmolecule

Gene 1

Gene 2

Gene 3

DNAtemplatestrand

TRANSCRIPTION

TRANSLATION

mRNA

Protein

Codon

Amino acid

TranscriptionTranscription

The process of building an The process of building an RNA copy of a DNA RNA copy of a DNA sequencesequenceDNA is too big to leave the DNA is too big to leave the nucleusnucleusmRNA is a copy of the DNA mRNA is a copy of the DNA sequencesequence

mRNAmRNA

Also known as messenger Also known as messenger RNARNA

Takes the code out into the Takes the code out into the cell for protein synthesiscell for protein synthesis

Steps of TranscriptionSteps of Transcription

InitiationInitiation RNA polymerase binds to a promoter (specific RNA polymerase binds to a promoter (specific

nucleotide sequence: TATA box)nucleotide sequence: TATA box)

ElongationElongation RNA polymerase adds free RNA nucleotides RNA polymerase adds free RNA nucleotides

that are complementary to the DNA strandthat are complementary to the DNA strand

TerminationTerminationRNA polymerase releases at a termination RNA polymerase releases at a termination sequencesequence

Steps of TranscriptionSteps of Transcription

Promoter Transcription unit

DNAStart point

RNA polymerase

553

3

Initiation

33

1

RNAtranscript

5 5

UnwoundDNA

Template strandof DNA

2 Elongation

RewoundDNA

5

5 5 3 3 3

RNAtranscript

3 Termination

5

5 5 33

3Completed RNA transcript

Genetic CodeGenetic CodeThe nearly universal The nearly universal genetic codegenetic code identifies the specific amino acids coded identifies the specific amino acids coded for by each three-nucleotide mRNA for by each three-nucleotide mRNA codoncodon..

TranslationTranslation

Steps of TranslationSteps of Translation During During translationtranslation, amino acids are , amino acids are

assembled from information encoded in assembled from information encoded in mRNA. mRNA.

As the mRNA codons move through the As the mRNA codons move through the ribosome, tRNAs add specific amino acids ribosome, tRNAs add specific amino acids to the growing polypeptide chain. to the growing polypeptide chain.

The process continues until a stop codon is The process continues until a stop codon is reached and the newly made protein is reached and the newly made protein is released.released.

RibosomeRibosome

Polypeptide

Ribosome

Aminoacids

tRNA withamino acidattached

tRNA

Anticodon

TrpPhe Gly

Codons 35

mRNA

Translation: Assembling Translation: Assembling ProteinsProteins

DNA Errors in ReplicationDNA Errors in Replication

Changes in DNA are called Changes in DNA are called mutationsmutations. .

DNA proofreading and repair prevent DNA proofreading and repair prevent many replication errors.many replication errors.

DNA Replication and CancerDNA Replication and Cancer Unrepaired mutations that affect genes that Unrepaired mutations that affect genes that

control cell division can cause diseases such control cell division can cause diseases such as cancer.as cancer.

The Human GenomeThe Human Genome

The entire gene sequence of the human The entire gene sequence of the human genomegenome, the complete genetic content, , the complete genetic content, is now known. is now known.

To learn where and when human cells To learn where and when human cells use each of the proteins coded for in the use each of the proteins coded for in the approximately 30,000 genes in the approximately 30,000 genes in the human genome will take much more human genome will take much more analysis. analysis.