chapters 14: dna structure & function ch.15 from dna to protein occ bio-161 by dave werner

Chapters 14: DNA Structure Chapters 14: DNA Structure & Function& Function

Ch.15 From DNA to ProteinCh.15 From DNA to Protein

OCC BIO-161OCC BIO-161

By Dave WernerBy Dave Werner

Chapters 14 & 15 Overview Chapters 14 & 15 Overview

DNA – ReplicationDNA – Replication

RNA - TranscriptionRNA - Transcription

Protein Synthesis - TranslationProtein Synthesis - Translation

Intro VideoIntro Video

Basic DNA ReplicationBasic DNA Replication

DNA ReplicationDNA Replication

Shadow Labs Video 4:27Shadow Labs Video 4:27

DNADNA

Ultimately the genetic source of this Ultimately the genetic source of this amazing diversity is deoxyribonucleic acid. amazing diversity is deoxyribonucleic acid. The primary function of DNA in organisms The primary function of DNA in organisms is to store and transmit the genetic is to store and transmit the genetic information that tells cells which proteins information that tells cells which proteins to make and when to make them.to make and when to make them.Proteins in turn form the structural units of Proteins in turn form the structural units of cells and help control chemical processes cells and help control chemical processes within cells.within cells.

Structure of DNAStructure of DNA

DNA is an organic compound made up of DNA is an organic compound made up of 2 long chains of nucleotides2 long chains of nucleotides

DNA is made up of DNA is made up of – 1. 1. sugar moleculesugar molecule – deoxyribose – deoxyribose– 2. 2. phosphate groupphosphate group – consists of phosphorus – consists of phosphorus

atom surrounded by oxygen atoms.atom surrounded by oxygen atoms.– 3. 3. nitrogen-containing basenitrogen-containing base

Structure of DNA – Nitrogen BasesStructure of DNA – Nitrogen Bases

The four nitrogen-containing bases found The four nitrogen-containing bases found in DNA nucleotides are:in DNA nucleotides are:

AdenineAdenine

GuanineGuanine

CytosineCytosine

ThymineThymine– A G C T A G C T


In 1953, James In 1953, James Watson and Francis Watson and Francis Crick suggested a Crick suggested a model for the model for the structure of DNA. structure of DNA. This shape is known This shape is known as the double helixas the double helix

Rosalind Franklin’s WorkRosalind Franklin’s WorkWas an expert in x-ray crystallographyWas an expert in x-ray crystallography

Used this technique to examine DNA fibers Used this technique to examine DNA fibers

Concluded that DNA was some sort of helixConcluded that DNA was some sort of helix


Individual nucleotides are connected by Individual nucleotides are connected by covalentcovalent bondsbonds between the deoxyribose between the deoxyribose sugar and the phosphate molecules sugar and the phosphate molecules

The alternating deoxyribose sugar and The alternating deoxyribose sugar and phosphate molecules form a “phosphate molecules form a “backbonebackbone” to ” to which the nitrogen-containing bases which the nitrogen-containing bases attach.attach.


By facing toward the center, the bases on By facing toward the center, the bases on one chain of DNA face the bases of the one chain of DNA face the bases of the other chain of DNAother chain of DNA

Form Form hydrogen bondshydrogen bonds..

Complementary Base PairingComplementary Base Pairing

Cytosine pairs with Cytosine pairs with Guanine Guanine C-GC-G

Adenine pairs with Adenine pairs with Thymine Thymine A-TA-T

These pairs are These pairs are known as known as complementary base complementary base pairspairs..

Nucleotide BasesNucleotide Bases

phosphate group

deoxyribose

ADENINE (A)

THYMINE (T)

CYTOSINE (C)

GUANINE (G)

DNADNA

Structure of DNA VideoStructure of DNA Video

Replication of DNAReplication of DNA

ReplicationReplication is the process of is the process of copying DNAcopying DNA

The 2 nucleotide chains separate by The 2 nucleotide chains separate by unwindingunwinding, and each chain serves as a , and each chain serves as a templatetemplate for a new nucleotide chain. for a new nucleotide chain.

Replication forkReplication fork is the point at which the 2 is the point at which the 2 chains separate chains separate

DNA DNA ReplicationReplication

newnew old old

Each parent Each parent

strand remains strand remains

intactintact

Every DNA Every DNA

molecule is half molecule is half

““oldold” and half ” and half

““newnew””


The chains are separated by enzymes The chains are separated by enzymes called called helicaseshelicasesDNA polymerasesDNA polymerases are enzymes that bind are enzymes that bind to the separated chains of DNAto the separated chains of DNAAs DNA polymerases move along the As DNA polymerases move along the separated chains, new chains of DNA are separated chains, new chains of DNA are assembled using nucleotides in the assembled using nucleotides in the surrounding medium that are surrounding medium that are complementary to the existing DNA chainscomplementary to the existing DNA chains


When replication is completed, When replication is completed, 2 new 2 new exact copies of the original DNA exact copies of the original DNA molecule are producedmolecule are produced and the cell is and the cell is ready to undergo cell divisionready to undergo cell division

What phase of the cell cycle does this What phase of the cell cycle does this happen?happen?

Accuracy and RepairAccuracy and Repair

The The # of errors# of errors and and mutationsmutations in DNA in DNA replication is reduced as replication is reduced as enzymesenzymes proofreadproofread DNA and DNA and repairrepair errors. errors.

1 error in 10,000 goes from 1 in 1 billion 1 error in 10,000 goes from 1 in 1 billion b/c of proofreading & repair b/c of proofreading & repair

Error = Error = mutationmutation

Mutations can occur from chemicals, UV, Mutations can occur from chemicals, UV, and other agents.and other agents.

Ch.14 From DNA to ProteinCh.14 From DNA to Protein

Recall that the nucleotides in DNA molecules Recall that the nucleotides in DNA molecules are grouped into genes that contain the are grouped into genes that contain the information needed to make specific proteins. information needed to make specific proteins. In eukaryotes, the genes detecting protein In eukaryotes, the genes detecting protein production are in the nucleus, and the enzymes production are in the nucleus, and the enzymes and amino acid building blocks for protein and amino acid building blocks for protein production are in the cytosol. production are in the cytosol. Nucleic acid called Nucleic acid called ribonucleic acidribonucleic acid is is responsible for the movement of genetic responsible for the movement of genetic information information from the DNA in the nucleus to the from the DNA in the nucleus to the site of protein synthesis in the cytosolsite of protein synthesis in the cytosol

Structure of RNAStructure of RNA

RNA structure is similar to that of DNA, RNA structure is similar to that of DNA, except:except:

The sugar in RNA is The sugar in RNA is riboseribose, not , not deoxyribosedeoxyribose

UracilUracil, a nitrogen containing pyrimidine , a nitrogen containing pyrimidine base, replaces base, replaces thyminethymine in RNA in RNA

DNA vs. RNADNA vs. RNADNA BasesDNA Bases RNA BasesRNA Bases

Uricil Base (U) Thymine Base (T)

3 Types of RNA3 Types of RNA

1.1. Messenger RNA Messenger RNA (mRNA) (mRNA) consists of consists of RNA nucleotides in the form of a single RNA nucleotides in the form of a single uncoiled chain. mRNA carries genetic uncoiled chain. mRNA carries genetic information from the DNA in the nucleus to information from the DNA in the nucleus to the cytosol of a eukaryotic cell.the cytosol of a eukaryotic cell.


2. 2. Transfer RNA (tRNA)Transfer RNA (tRNA) consists of a consists of a single chain of about 80 RNA nucleotides single chain of about 80 RNA nucleotides folded into a hairpin shape that binds to folded into a hairpin shape that binds to specific amino acids. There are about 45 specific amino acids. There are about 45 varieties of tRNAvarieties of tRNA


3. 3. Ribosomal RNA (rRNA)Ribosomal RNA (rRNA) – the most – the most abundant form of RNA. rRNA consists of abundant form of RNA. rRNA consists of RNA nucleotides in a globular form. RNA nucleotides in a globular form. Joined by proteins, rRNA makes up the Joined by proteins, rRNA makes up the ribosomes where proteins are made ribosomes where proteins are made

TranscriptionTranscription

Video ClipVideo Clip

TranscriptionTranscription is the process by which is the process by which genetic information is genetic information is copied from DNA to copied from DNA to RNA.RNA.

RNA polymeraseRNA polymerase, the primary , the primary transcription enzyme, synthesizes RNA transcription enzyme, synthesizes RNA copies of specific sequences of DNAcopies of specific sequences of DNA

Gene TranscriptionGene Transcription

transcribed DNA winds up again

DNA to be transcribed unwinds

mRNAtranscript

RNA polymerase


RNA polymerase initiates RNA RNA polymerase initiates RNA transcription by binding to specific regions transcription by binding to specific regions of DNA called of DNA called promoterspromoters

The The promoterpromoter marks the marks the beginningbeginning of the of the DNA chain that will be transcribed DNA chain that will be transcribed


When RNA polymerase binds to a When RNA polymerase binds to a promoter, the DNA molecule in that region promoter, the DNA molecule in that region separates.separates.

Only one of the separated DNA chains Only one of the separated DNA chains called the template is used in transcriptioncalled the template is used in transcription


RNA polymerase attaches to the RNA polymerase attaches to the first DNA first DNA nucleotidenucleotide of the template chain of the template chain

Then it begins Then it begins adding complementary adding complementary RNA nucleotidesRNA nucleotides to the newly forming to the newly forming RNA moleculeRNA molecule

The The base pairing rulesbase pairing rules are identical to are identical to those in DNA replication, except that those in DNA replication, except that uraciluracil pairs with pairs with adenineadenine


Transcription continues one nucleotide at Transcription continues one nucleotide at a time until the RNA polymerase reaches a time until the RNA polymerase reaches a DNA region called the a DNA region called the termination termination signalsignal..

Termination signalTermination signal is a specific sequence is a specific sequence of nucleotides that marks the of nucleotides that marks the end of a end of a genegene..


At the termination signal, RNA polymerase At the termination signal, RNA polymerase releases both the DNA molecule and the releases both the DNA molecule and the newly formed RNA moleculenewly formed RNA molecule

All three types of RNA are transcribed in All three types of RNA are transcribed in this processthis process..

Adding NucleotidesAdding Nucleotides

growing RNA transcript5’

3’5’

3’

direction of transcription

Transcript ModificationTranscript ModificationFig. 14.4Fig. 14.4

unit of transcription in a DNA strand

exon intron

mature mRNA transcript

poly-A tail

5’

5’ 3’

3’

snipped out

snipped out

exon exonintron

cap

transcription into pre-mRNA

3’ 5’


The products of transcription are the The products of transcription are the different types of RNA molecules, different types of RNA molecules, including including mRNA, tRNA, and rRNAmRNA, tRNA, and rRNA..

Following transcription, Following transcription, mRNAmRNA moves moves through the pores of the nuclear through the pores of the nuclear membrane into the membrane into the cytosolcytosol of the cell of the cell where where it will direct the synthesis or it will direct the synthesis or translation of the proteintranslation of the protein..

Protein SynthesisProtein Synthesis

The production of proteins is also called The production of proteins is also called protein synthesisprotein synthesis. .

The amount and kind of proteins that are The amount and kind of proteins that are produced in a cell determine the structure produced in a cell determine the structure and function of the cell. and function of the cell.

In this way, In this way, proteins carry out the genetic proteins carry out the genetic instructions encoded in an organism’s instructions encoded in an organism’s DNA.DNA.

Protein Structure and CompositionProtein Structure and Composition

Proteins are made up of one or more Proteins are made up of one or more polypeptidespolypeptides, each which consists of a , each which consists of a specific sequence of specific sequence of amino acidsamino acids linked linked together by together by peptide bondspeptide bonds..

The sequence of the amino acids The sequence of the amino acids determines how the polypeptides determines how the polypeptides will twist will twist andand fold into the three-dimensional fold into the three-dimensional structure of the proteinstructure of the protein

The Genetic CodeThe Genetic Code

During During protein synthesisprotein synthesis, the sequence of , the sequence of nucleotidesnucleotides in an mRNA transcript is in an mRNA transcript is translated into a sequence of translated into a sequence of amino acidsamino acids..Genetic CodeGenetic Code is the correlation between a is the correlation between a nucleotidenucleotide sequence and sequence and amino acidamino acid sequence sequence This genetic code is used by most This genetic code is used by most organisms to translate mRNA transcripts organisms to translate mRNA transcripts into into proteinsproteins

Genetic CodeGenetic Code

Set of Set of 6464 base triplets base triplets

CodonsCodons– Nucleotide bases read in Nucleotide bases read in

blocks of blocks of threethree

6161 specify amino acids specify amino acids

3 stop translation3 stop translation

Code Is RedundantCode Is Redundant

Twenty kindsTwenty kinds of amino acids are specified by of amino acids are specified by

61 codons61 codons

Most amino acids can be specified by more Most amino acids can be specified by more

than one codonthan one codon

Six codons specify leucineSix codons specify leucine

– UUA, UUG, CUU, CUC, CUA, CUGUUA, UUG, CUU, CUC, CUA, CUG

Redundant?Redundant?(Genetic Code Secret Decoder Ring)(Genetic Code Secret Decoder Ring)

The Genetic CodeThe Genetic Code

CodonsCodons are 3 mRNA nucleotides which are 3 mRNA nucleotides which code for a specific amino acid.code for a specific amino acid.

The The Start Codon (AUG),Start Codon (AUG), which also codes which also codes for the amino acid methionine, engages a for the amino acid methionine, engages a ribosome to start translating an mRNA ribosome to start translating an mRNA moleculemolecule

Stop Codons (UAA, UAG, UGA)Stop Codons (UAA, UAG, UGA) cause the cause the ribosome to stop translating an mRNAribosome to stop translating an mRNA

TranslationTranslation

TranslationTranslation is the process of is the process of assembling assembling polypeptidespolypeptides from information encoded in from information encoded in mRNAmRNA

This process starts when This process starts when mRNA leaves mRNA leaves the nucleusthe nucleus through pores in the nuclear through pores in the nuclear membrane.membrane.

The mRNA then migrates to a The mRNA then migrates to a ribosomeribosome in in to to cytosolcytosol


Amino acids floating freely in the cytosol Amino acids floating freely in the cytosol are are transportedtransported to the ribosomes by to the ribosomes by tRNAtRNA molecules.molecules.

tRNA anticodontRNA anticodon is complementary to and is complementary to and pairs with the corresponding mRNA pairs with the corresponding mRNA codon.codon.


The same base pairing rules apply for The same base pairing rules apply for translationtranslation as they did for as they did for transcriptiontranscription

tRNA anticodon AAA binds with mRNA tRNA anticodon AAA binds with mRNA codon UUU and forms the amino acid codon UUU and forms the amino acid phenlythalinephenlythaline


The assembly of a polypeptide begins The assembly of a polypeptide begins when a ribosome attaches to the when a ribosome attaches to the start start codon (AUG)codon (AUG) on an mRNA transcript. on an mRNA transcript.

The start codon pairs with the anticodon The start codon pairs with the anticodon UAC on a tRNA.UAC on a tRNA.

Protein AssemblyProtein Assembly

Amino Acids attach to Translated AA w/ a Amino Acids attach to Translated AA w/ a Covalent bond = Covalent bond = Peptide BondPeptide Bond

This creates a polypeptide chain = This creates a polypeptide chain = ProteinProtein

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rvie

wO

verv

iew

Transcription

Translation

mRNA rRNA tRNA

Mature mRNA transcripts

ribosomal subunits

mature tRNA

chapters 14: dna structure & function ch.15 from dna to protein occ bio-161 by dave werner

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