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• Human chromosomes: 50->250 million base pairs.• Average gene: 3000 base pairs.• <5% of DNA codes for protein.

What is a Gene? What is a Gene? • Short stretch of DNA on chromosome.Short stretch of DNA on chromosome.• Two parts:Two parts:

• Information in genes used to make proteins.Information in genes used to make proteins.• Two Stages:Two Stages:

• TranscriptionTranscription• TranslationTranslation

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DNA

Coding region

Regulatory region

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12-3 Protein Synthesis12-3 Protein Synthesis

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DNADNA vs.vs. RNARNA

Double strandedDouble stranded Sugar = deoxyriboseSugar = deoxyribose Thymine (no Uracil)Thymine (no Uracil)

Stays in nucleusStays in nucleus One typeOne type

Same copy in the Same copy in the cell all the timecell all the time

Single strandedSingle stranded Sugar = riboseSugar = ribose Uracil (instead of Uracil (instead of

Thymine)Thymine) Nucleus & cytoplasmNucleus & cytoplasm 3 types (mRNA, tRNA, 3 types (mRNA, tRNA,

rRNA)rRNA) Disposable copiesDisposable copies

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Ribose vs. DeoxyriboseRibose vs. Deoxyribose

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RNARNA many functions but mostly just many functions but mostly just

protein synthesisprotein synthesis

three main types of RNA: three main types of RNA: mmessenger RNA, essenger RNA, rribosomal RNA, ibosomal RNA, and and ttransfer RNA ransfer RNA

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Types of RNATypes of RNA

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mRNAmRNA RNA molecules that carry copies of RNA molecules that carry copies of

the DNA instructions = mRNAthe DNA instructions = mRNA messenger RNAmessenger RNA (mRNA) = serve as (mRNA) = serve as

“messengers” from DNA to the rest “messengers” from DNA to the rest of the cell of the cell

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Transcription & Transcription & TranslationTranslation

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TranscriptionTranscription (DNA (DNA mRNA)mRNA)

RNA molecules are produced by copying RNA molecules are produced by copying partpart of the nucleotide sequence of DNA into a of the nucleotide sequence of DNA into a complementary sequence in RNAcomplementary sequence in RNA

required enzyme = required enzyme = RNA polymeraseRNA polymerase

1.1. RNA polymerase binds to DNA (in nucleus)RNA polymerase binds to DNA (in nucleus)

2.2. separates the DNA strandsseparates the DNA strands

3.3. RNA polymerase then uses one strand of DNA RNA polymerase then uses one strand of DNA as a template as a template

4.4. nucleotides are assembled into a strand of nucleotides are assembled into a strand of mRNA mRNA

Transcription Animation

TRANSCRIPTIONTRANSCRIPTIONSimilar to DNA replication, but Similar to DNA replication, but different.different.1. Copies only one of the two 1. Copies only one of the two strands.strands.2. Makes a copy as RNA, not DNA.2. Makes a copy as RNA, not DNA.

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Where does RNA start?Where does RNA start?csadaksjdfllasdailsdflRaiseyourhandifyoucanreadthis.aksdjfjasdkjaskcsadaksjdfllasdailsdflRaiseyourhandifyoucanreadthis.aksdjfjasdkjaskklasdjfkkjajdfiodlskjklasdjfkkjajdfiodlskj

Need punctuation to identify where coding Need punctuation to identify where coding region begins and ends:region begins and ends:promoterspromoters - signals in DNA that indicate - signals in DNA that indicate where the enzyme should bind (“start where the enzyme should bind (“start sequence”).sequence”).Similar signals in DNA cause transcription to Similar signals in DNA cause transcription to stopstop when the new RNA molecule is when the new RNA molecule is completed. completed.

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RNA EditingRNA Editing IntronIntron = intervening sequence of DNA; = intervening sequence of DNA;

does does notnot code for a protein code for a protein ExonExon = expressed sequence of DNA; = expressed sequence of DNA;

codes for a proteincodes for a protein When RNA molecules are formed, both When RNA molecules are formed, both

the the intronsintrons and the and the exonsexons are copied are copied from the DNA from the DNA – introns are introns are cut outcut out of RNA molecules while of RNA molecules while

they are still in the nucleus they are still in the nucleus – exons are then spliced back together to exons are then spliced back together to

form the final mRNA form the final mRNA

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The Genetic CodeThe Genetic Code

Proteins = long chains of amino acids Proteins = long chains of amino acids

(polypeptides)(polypeptides) polypeptide = combination of any or polypeptide = combination of any or

all of the 20 different amino acids all of the 20 different amino acids properties of proteinsproperties of proteins are are

determined by the order in which determined by the order in which different amino acids are joined different amino acids are joined together to produce polypeptides together to produce polypeptides

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The “language” of The “language” of mRNAmRNA instructions instructions is called the genetic code is called the genetic code

RNA contains four different bases: A, RNA contains four different bases: A, U, C, and G U, C, and G

Letters read “3” at a time = codonLetters read “3” at a time = codon Codon Codon = a group of three = a group of three

nucleotides on nucleotides on mmessenger RNA that essenger RNA that specify a particular amino acid. specify a particular amino acid.

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Translation Translation (mRNA(mRNA tRNA tRNA amino acid amino acid

chain)chain)Occurs at the RibosomeOccurs at the RibosomemRNA = instructions for the mRNA = instructions for the

order of the amino acid order of the amino acid sequencesequence

Ribosome = reads the Ribosome = reads the instructions of the mRNAinstructions of the mRNA

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TranslationTranslation

DNA/RNA

AdenineCytosineGuanineThymine/Uracil

Amino AcidAlanine ArginineAsparagine Aspartate Cysteine GlutamineGlutamate GlycineHistidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline SerineThreonine TyrosineTryptophan Valine

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rRNArRNA RibosomesRibosomes are made up of several are made up of several

dozen proteins, as well as a form of dozen proteins, as well as a form of RNA known as RNA known as ribosomal RNAribosomal RNA (rRNA). (rRNA).

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tRNAtRNA

During the construction of a protein, a During the construction of a protein, a third type of RNA molecule transfers third type of RNA molecule transfers each amino acid to the ribosome each amino acid to the ribosome – as specified by coded as specified by coded

messages in mRNA. messages in mRNA. These RNA molecules These RNA molecules

are known as are known as

transfer RNAtransfer RNA (tRNA). (tRNA).

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Steps of TranslationSteps of Translation

1.1. mRNA is released from the nucleus mRNA is released from the nucleus enters cytoplasmenters cytoplasm

2.2. mRNA attaches to the ribosomemRNA attaches to the ribosome

3.3. mRNA codons move through the mRNA codons move through the ribosomeribosome proper amino acid proper amino acid brought by tRNAbrought by tRNA

4.4. Amino acids are bound together Amino acids are bound together polypeptide chainpolypeptide chain

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Each tRNA carries only Each tRNA carries only oneone type of type of amino acidamino acid

The three bases on tRNA = The three bases on tRNA = anticodonanticodon (complementary to mRNA)(complementary to mRNA)

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The ribosome The ribosome forms peptide bondsforms peptide bonds between the neighboring amino acidsbetween the neighboring amino acids

It also breaks the bonds between tRNA It also breaks the bonds between tRNA and the amino acidsand the amino acids

Translation ends when a “stop” codon is Translation ends when a “stop” codon is reachedreached

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Translation Animation

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Bases in DNA/RNA form Bases in DNA/RNA form triplet codetriplet code

Second BaseU C A G

First base

U UUU Phe (F) UCUSer (S)

UAUTyr (Y)

UGUCys (C)

U

Third base

UUC UCC UAC UGC CUUA Leu (L) UCA UAA Stop UGA Stop AUUG UCG UAG Stop UGG Trp (W) G

C CUU

Leu (L)

CCU

Pro (P)

CAUHis (H)

CGU

Arg (R)

UCUC CCC CAC CGC CCUA CCA CAA

Gln (Q)CGA A

CUG CCG CAG CGG G

A AUUIle (I)

ACU

Thr (T)

AAUAsn (N)

AGUSer (S)

UAUC ACC AAC AGC CAUA ACA AAA

Lys (K)AGA

Arg (R)A

AUG Met (M) Start

ACG AAG AGG G

G GUU

Val (V)

GCU

Ala (A)

GAUAsp (D)

GGU

Gly (G)

UGUC GCC GAC GGC CGUA GCA GAA

Glu (E)GGA A

GUG GCG GAG GGG G

Codon Table:

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What amino acids are What amino acids are made?made?

Use the mRNA strand on the Genetic Use the mRNA strand on the Genetic Code ChartCode Chart

DNA: TAC AAA CAC GGA CCA ACTDNA: TAC AAA CAC GGA CCA ACT (coding strand)(coding strand)

mRNA: AUG UUU GUG CCU GGU UGA mRNA: AUG UUU GUG CCU GGU UGA tRNA: UAC AAA CAC GGA CCA ACUtRNA: UAC AAA CAC GGA CCA ACU Amino acids: Methionine – Amino acids: Methionine –

Phenylalanine – Phenylalanine – Valine - Proline - Glycine - STOPValine - Proline - Glycine - STOP

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