Chapters 13: DNA Structure & Function Ch.14 From DNA to Protein
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Transcript of Chapters 13: DNA Structure & Function Ch.14 From DNA to Protein
Chapters 13: DNA Structure Chapters 13: DNA Structure & Function& Function
Ch.14 From DNA to ProteinCh.14 From DNA to Protein
OCC BIO-114OCC BIO-114
By Dave WernerBy Dave Werner
Chapters 13 & 14 Overview Chapters 13 & 14 Overview
DNA – ReplicationDNA – Replication
RNA - TranscriptionRNA - Transcription
Protein Synthesis - TranslationProtein Synthesis - Translation
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 DNA (fig.13-5)Structure of DNA (fig.13-5)
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 (fig.13-4) (fig.13-4)
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
Structure of DNA (fig.13.5)Structure of DNA (fig.13.5)
Structure of DNAStructure of DNA
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
Structure of DNAStructure of DNA
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.
Structure of DNAStructure of DNA
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)
Replication of DNA (fig.13-6)Replication of DNA (fig.13-6)
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””
Replication of DNAReplication of DNA
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
Replication of DNAReplication of DNA
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.
3 Types of RNA3 Types of RNA
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 Types of RNA3 Types of RNA
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
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
TranscriptionTranscription
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
TranscriptionTranscription
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
TranscriptionTranscription
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
TranscriptionTranscription
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..
TranscriptionTranscription
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’
TranscriptionTranscription
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
TranslationTranslation
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.
TranslationTranslation
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
TranslationTranslation
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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Transcription
Translation
mRNA rRNA tRNA
Mature mRNA transcripts
ribosomal subunits
mature tRNA