DNA and RNA. 2 Replication Facts DNA has to be copied before a cell dividesDNA has to be copied...

DNA and RNA

Replication FactsReplication Facts

• DNA has to be copied DNA has to be copied before a cell dividesbefore a cell divides

• DNA is copied during DNA is copied during the the SS or synthesis phase or synthesis phase of of interphaseinterphase

• New cells will need New cells will need identical identical DNA strandsDNA strands

Synthesis Phase (S Synthesis Phase (S phase)phase)

• S phase during interphase of the cell cycle

• Nucleus of eukaryotes

Mitosis-prophase-metaphase-anaphase-telophase

Sphase

interphase

DNA replication takesDNA replication takesplace in the S phase.place in the S phase.

copyright cmassengale

HOW IS DNA COPIED?Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif

The structure of DNA explains how it can be copied.

Each strand has all the info needed to construct the __________other half.

If strands are separated,_____________ rules allowyou to fill in the complementary bases.

matching

base-pairing

DNA ReplicationDNA Replication

• Begins atBegins at Origins of ReplicationOrigins of Replication• Two strands open forming Two strands open forming

Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)

• New strands grow at the forksNew strands grow at the forks

ReplicationReplicationForkFork

Parental DNA MoleculeParental DNA Molecule

5’copyright cmassengale

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

Sites where strand separation and replication occur are called _____________replication forks

DNA ReplicationDNA Replication• As the 2 DNA strands open at As the 2 DNA strands open at

the origin, the origin, Replication Replication BubblesBubbles form form

• Prokaryotes (bacteria) have a single bubble

• Eukaryotic chromosomes have MANY bubbles

Bubbles Bubbles

DNA ReplicationDNA Replication

• Enzyme Enzyme HelicaseHelicase unwinds and separates unwinds and separates the 2 DNA strands by the 2 DNA strands by breaking the breaking the weak weak hydrogen bondshydrogen bonds

• Single-Strand Binding Single-Strand Binding ProteinsProteins attach and keep the 2 DNA strands separated and untwisted

DNA ReplicationDNA Replication• Enzyme Enzyme TopoisomeraseTopoisomerase

attaches to the 2 forks of the bubble to relieve stressrelieve stress on the DNA moleculeDNA molecule as it separatesEnzyme

Enzyme

DNA ReplicationDNA Replication• BeforeBefore new DNA strands can

form, there must be RNA RNA primersprimers present to start the addition of new nucleotides

• PrimasePrimase is the enzyme that synthesizes the RNA Primer

• DNA polymerase can then add the new nucleotides

11copyright cmassengale

DNA ReplicationDNA Replication• DNA polymeraseDNA polymerase can only add can only add

nucleotides to the nucleotides to the 33 ’’ end end of of the DNA the DNA

• This causes the This causes the NEWNEW strand to strand to be built in a be built in a 55 ’’ to 3 to 3’’ direction direction

RNARNAPrimerPrimerDNA PolymeraseDNA Polymerase

NucleotideNucleotide

5’ 3’

Direction of ReplicationDirection of Replicationcopyright cmassengale

Remember HOW the Remember HOW the Carbons Are Numbered!Carbons Are Numbered!

OO=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

SugarSugar(deoxyribose)(deoxyribose)

Remember the Strands are Remember the Strands are AntiparallelAntiparallel

Synthesis of the New DNA Synthesis of the New DNA StrandsStrands

• The The Leading StrandLeading Strand is synthesized as a single single strand strand from the point of origin toward the opening replication fork

RNARNAPrimerPrimerDNA PolymeraseDNA PolymeraseNucleotidesNucleotides

3’5’

Synthesis of the New DNA Synthesis of the New DNA StrandsStrands

• The The Lagging StrandLagging Strand is is synthesized discontinuouslydiscontinuously against overall direction of replication

• This strand is made in MANY short segments It is replicated from the replication fork toward the origin

RNA PrimerRNA Primer

Leading StrandLeading Strand

DNA PolymeraseDNA Polymerase

Lagging StrandLagging Strand

3’ copyright cmassengale

Lagging Strand Lagging Strand SegmentsSegments

• Okazaki FragmentsOkazaki Fragments - - series of short segments on the lagging strandlagging strand

• Must be joined together by Must be joined together by an an enzymeenzyme

Lagging Strand

RNARNAPrimerPrimer

DNADNAPolymerasePolymerase

Okazaki FragmentOkazaki Fragment

Joining of Okazaki FragmentsJoining of Okazaki Fragments

• The enzyme The enzyme LigaseLigase joins the joins the Okazaki fragments together Okazaki fragments together to make one strandto make one strand

Lagging Strand

Okazaki Fragment 2Okazaki Fragment 2

DNA ligaseDNA ligase

Okazaki Fragment 1Okazaki Fragment 1

Replication of StrandsReplication of StrandsReplication Fork

Point of Origin

Proofreading New DNAProofreading New DNA

• DNA polymerase initially DNA polymerase initially makes about makes about 1 in 10,0001 in 10,000 base base pairing errorspairing errors

• EnzymesEnzymes proofread and proofread and correct these mistakescorrect these mistakes

• The new error rate for DNA The new error rate for DNA that has been proofread is that has been proofread is 1 1 in 1 billionin 1 billion base pairing errors base pairing errors

REPLICATION STEPS1.Enzymes “unzip” molecule by breaking_______________ that hold the strands together and unwind it.

2. _______________ joins nucleotides using original strand as template and______________for errors.

3. Copying happens in ________ directionsalong the two strands & in __________ places at once.

Hydrogen bonds

DNA polymerase

spell checks

oppositemultiple

Semiconservative Model of Semiconservative Model of ReplicationReplication

• Idea presented by Idea presented by Watson & CrickWatson & Crick• TheThe two strands of the parental

molecule separate, and each acts as a template for a new complementary strand

• New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA

Parental DNA

DNA Template

New DNA

DNA Damage & DNA Damage & RepairRepair

• Chemicals & ultraviolet radiation damage the DNA in our body cells

• Cells must continuously repair DAMAGED DNA

• Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA

• DNA polymerase and DNA ligase replace and bond the new nucleotides together

Question:Question:

•What would be the complementary DNA strand for the following DNA sequence?

DNA 5DNA 5’’-CGTATG-3-CGTATG-3’’copyright cmassengale

Answer:Answer:

DNA 5DNA 5’’-CGTATG-3-CGTATG-3’’DNA 3DNA 3’’-GCATAC-5-GCATAC-5’’

REPLICATIONANIMATION

RNA and PROTEIN SYNTHESIS

DNADNA

•DNA contains genes, sequences of nucleotide bases

•These Genes code for polypeptides (proteins)

•Proteins are used to build cells and do much of the work inside cells

Genes & ProteinsGenes & Proteins

Proteins are made of amino acids linked together by peptide bonds

20 different amino acids exist

Amino Acid StructureAmino Acid Structure

PolypeptidesPolypeptides

•Amino acid chains are called polypeptides

DNA Begins the DNA Begins the ProcessProcess

• DNA is found inside the nucleus• Proteins, however, are made in

the cytoplasm of cells by organelles called ribosomes

• Ribosomes may be free in the cytosol or attached to the surface of rough ER

Starting with DNAStarting with DNA• DNA DNA ‘‘s codes code must be must be copiedcopied

and taken to the cytosoland taken to the cytosol• In the cytoplasm, this In the cytoplasm, this code code

must be readmust be read so so amino amino acidsacids can be assembled to can be assembled to make polypeptides make polypeptides (proteins)(proteins)

• This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS

Roles of RNA and DNA

•DNA is the MASTER PLAN

•RNA is the BLUEPRINT of the

Master Plancopyright cmassengale

RNA Differs from DNARNA Differs from DNA

• RNA has a sugar RNA has a sugar riboseribose

DNA has a sugar DNA has a sugar deoxyribosedeoxyribose

Other DifferencesOther Differences

• RNA contains RNA contains the base the base uracil uracil (U(U))DNA has DNA has thymine (T)thymine (T)

• RNA molecule is RNA molecule is single-strandedsingle-strandedDNA is DNA is double-double-strandedstranded

DNAcopyright cmassengale

Structure of RNAStructure of RNA

RNA- the Other Nucleic Acid

Also made of ___________

Sugar is _______ insteadof deoxyribose.

RNA is _________ stranded

Contains _________ instead of thymine.

NUCLEOTIDES

RIBOSE

SINGLE

URACIL

http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg

3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS

_________________RNA (rRNA)Combines with proteins to form

ribosomes

_________________RNA (tRNA)transfers amino acids to the ribosomes transfers amino acids to the ribosomes

where proteins are synthesizedwhere proteins are synthesized((Matches m-RNA codon to add correctamino acids during protein synthesis)

_________________RNA (mRNA)copies DNA’s code (genetic information) copies DNA’s code (genetic information)

carries code from DNA to ribosomesrRNA and t-RNA images from © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reservedmRNA image from http://wps.prenhall.com/wps/media/tmp/labeling/1140654_dyn.gif

RIBOSOMAL

TRANSFER

MESSENGER

Messenger RNA• Long Straight

chain of Nucleotides

• Made in the Nucleus

• Copies DNA & leaves through nuclear pores

• Contains the Nitrogen Bases A, G, C, U ( no T )

Messenger RNA (mRNA)Messenger RNA (mRNA)• Carries the information for a Carries the information for a

specific proteinspecific protein• Made up of Made up of 500 to 1000 500 to 1000

nucleotides longnucleotides long• Sequence of 3 bases called Sequence of 3 bases called

codoncodon• AUGAUG – methionine or – methionine or start codonstart codon• UAA, UAG, or UGAUAA, UAG, or UGA – – stop codonsstop codons

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

• rRNA is a single rRNA is a single strand strand 100 to 100 to 3000 nucleotides3000 nucleotides longlong

• GlobularGlobular in shape in shape• Made inside the Made inside the

nucleusnucleus of a cell of a cell• Associates with Associates with

proteins to form proteins to form ribosomesribosomes

• Site of Site of protein protein SynthesisSynthesis

The Genetic Code

• A codon designates an amino acid

• An amino acid may have more than one codon

• There are 20 amino acids, but 64 possible codons

• Some codons tell the ribosome to stop translating

The Genetic Code •Use the

code by reading from the center to the outside•Example: AUG codes for Methionine

Remember the Remember the Complementary BasesComplementary Bases

On DNA: A-T C-GOn RNA: A-U C-G

Transfer RNA (tRNA)Transfer RNA (tRNA)• Clover-leaf shape• Single stranded molecule with

attachment site at one end for an amino acid

• Opposite end has three nucleotide bases called the anticodon

Transfer RNATransfer RNAamino acidamino acid

attachment siteattachment site

anticodonanticodoncopyright cmassengale

Codons and Anticodons

• The 3 bases of an anticodon are complementary to the 3 bases of a codon

• Example: Codon ACU

Anticodon UGA

Transcription Transcription and Translationand Translation

Pathway to Making a Pathway to Making a ProteinProtein

DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProteincopyright cmassengale

PROTEIN PROTEIN SYNTHESISSYNTHESIS

Protein SynthesisProtein Synthesis The production or synthesis of

polypeptide chains (proteins) Two phases:

Transcription & Translation mRNA must be processed

before it leaves the nucleus of eukaryotic cells

DNADNA RNARNA ProteinProtein

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

Pre-mRNA

Ribosome

Protein

EukaryotEukaryotic Cellic Cell

• The process of copying the sequence of one strand of DNA, the template strand

• mRNA copies the template strand

• Requires the enzyme RNA Polymerase

RNADNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Enzyme called _____________________ separates strands, then uses one strand as a template to assemble an RNA copy.

RNA POLYMERASE

Template Strand

Question:Question:

What would be the What would be the complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA sequence?

DNA 5DNA 5’’--GCGTATGGCGTATG-3-3’’

Answer:Answer:

•DNA 5DNA 5’’-GCGTATG-3-GCGTATG-3’’•RNA 3RNA 3’’-CGCAUAC-5-CGCAUAC-5’’

• During transcription, RNA polymerase binds to DNA and separates the DNA strands

• RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA

• Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA

• Called the TATA box• Specific base sequences act

as signals to stop• Called the termination signal

RNA PolymeraseRNA Polymerase

How does RNA POLYMERASE know where a gene starts and

stops?

Enzyme binds to places with specific DNA sequences called _______________.

PROMOTERS tell _________________where to start.

Signals at the end of the gene code cause transcription to _____ .

PROMOTERS

http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg

RNA POLYMERASE

mRNA ProcessingmRNA Processing

• After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional

• Introns, non-functional segments of DNA are snipped out of the chain

mRNA EditingmRNA Editing• Exons, segments of DNA that code for proteins, are then rejoined by the

enzyme ligase• A guanine triphosphate cap is added to the 5” end of the newly copied mRNA• A poly A tail is added to the 3’ end of the RNA• The newly processed mRNA can then leave the nucleus

65CAPTailNew Transcript

Result of TranscriptionResult of Transcription

mRNA Transcript

•mRNA leaves the nucleus through its pores and goes to the ribosomes

•Translation is the process of decoding the mRNA into a polypeptide chain

•Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

RibosomesRibosomes

•Made of a large and small subunit

•Composed of rRNA (40%) and proteins (60%)

•Have two sites for tRNA attachment --- P and A

Step 1- InitiationStep 1- Initiation

• mRNA transcript start codon AUG attaches to the small ribosomal subunit

• Small subunit attaches to large ribosomal subunitmRNA transcript

RibosomesRibosomes

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

Step 2 - Elongation• As ribosome moves, two tRNA

with their amino acids move into site A and P of the ribosome

• Peptide bonds join the amino acids

InitiationInitiation

mRNAmRNA

2-tRNA

1-tRNA

anticodon

hydrogenbonds codon

mRNAmRNA

1-tRNA 2-tRNA

U A C G

aa1 aa2

anticodon

hydrogenbonds codon

peptide bond

3-tRNA

ElongationElongation

mRNAmRNA

1-tRNA

2-tRNA

peptide bond

3-tRNA

Ribosomes move over one codon

(leaves)

mRNAmRNA

2-tRNA

peptide bonds

3-tRNA

4-tRNA

mRNAmRNA

2-tRNA

aa1aa2

peptide bonds

3-tRNA

4-tRNA

(leaves)

Ribosomes move over one codoncopyright cmassengale

mRNAmRNA

G C U A C U U C G

aa1aa2

peptide bonds

3-tRNA

4-tRNA

5-tRNA

mRNAmRNA

G C U A C U U C G

aa1aa2

peptide bonds

3-tRNA

4-tRNA

5-tRNA

Ribosomes move over one codoncopyright cmassengale

mRNAmRNA

A C A U G U

primaryprimarystructurestructureof a proteinof a protein

200-tRNA

terminatorterminator or stopor stop codoncodon

TerminationTermination

End Product –The Protein!End Product –The Protein!• The end products of protein

synthesis is a primary structure of a protein

• A sequence of amino acid bonded together by peptide bonds

aa2 aa3 aa4aa5

Messenger RNA (mRNA)Messenger RNA (mRNA)

methionine glycine serine isoleucine glycine alanine stopcodon

proteinprotein

A U G G G C U C C A U C G G C G C A U A AmRNAmRNA

startcodon

Primary structure of a proteinPrimary structure of a protein

aa1 aa2 aa3 aa4 aa5 aa6

peptide bonds

codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1

MASTER PLAN DNA stays safe in nucleus TRANSCRIPTION (DNA→ RNA)& PROCESSINGtakes place in nucleus

TRANSLATION (RNA→ proteins)takes place on ribosomes in cytoplasm

“Blueprints” of master plan are carried to building site

http://www.home-improvement-resource.com/images/architect.jpg

RNA’s require EDITING before use

Image by Riedell

WHY WASTE IT?

Why spend energy making a large RNAand then throw parts away?

May allow same gene to be used indifferent ways in different kinds of cells.

May have a role in evolution… allows small

changes in genes to have a big effect.

HOW CAN JUST 4 BASES GIVE DIRECTIONS TO MAKE 20 AMINO ACIDS?

Message is read in groups of 3 = _________

UCGCACGGU UCG-CAC-GGU

Codons represent different amino acids

Serine- Histidine- Glycine

Section 12-3

64 possible codons

Some amino acidshave more than onecodon.

START= _______

3 codons for _____

___________ on tRNA

matches up with________ on mRNA

ANTICODON

EACH tRNA carries onlyone kind of_____________amino acid

Figure 12–18 TranslationSection 12-3

Figure 12–18 Translation (continued)Section 12-3

GENES & PROTEINSProteins are the connection

betweenthe gene code in the DNA and how

thatgene is expressed.

A gene that codes for an enzyme (protein) to make a pigment can control the color of a flower.

A gene that codes for an enzyme (protein) adds carbohydrates to glycoproteins to produce your blood type.

Enzymes catalyze and regulate chemical reactions so proteins build and operate all cell components.

DNA → DNA ____________

DNA → RNA ____________

RNA→ Protein ___________

REPLICATION

TRANSCRIPTION

TRANSLATION

from to to make up

Concept MapSection 12-3

also called which functions to also called also called which functions towhich functions to

can be

from to to make up

Concept MapSection 12-3

also called which functions to also called also called which functions towhich functions to

can be

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

Let’s Practice!

http://learn.genetics.utah.edu/content/begin/dna/transcribe/

DNA and RNA. 2 Replication Facts DNA has to be copied before a cell dividesDNA has to be copied...

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