Protein Synthesis DNA Transcription and Translation.

Protein Synthesis

DNA Transcription and Translation

What is the purpose for proteins? We What is the purpose for proteins? We are made of protein!are made of protein!

• antibody: fight diseases

• Muscle contractions

• Enzymes

• Hormones

• Hair, feathers, beaks, nails, horns, etc.

• Egg whites

• Transport proteins: blood(hemoglobin)

Protein StructureProtein Structure

• Made up of amino acids

• Polypeptide- string of amino acids

• ONLY 20 amino acids are arranged in different orders to make a variety of proteins!!!! Amino acids are in the cytoplasm.

• Assembled on a ribosome

How Does Our Body Create Proteins from DNA?? Its in the nucleus!!!!!!

DNA

mRNA

Transcription

Introduction

The Central Dogma of Molecular Biology

Cell

Polypeptide(protein)

TranslationRibosome

DOGMA?

This central dogma(process) was develop by Crick.

This was a hypothesis on how the code was read from DNA then used to make proteins. Scientists did not like this term for this hypothesis because it sounds like a problem!

Central Dogma of Biology

The flow of information in the cell starts at DNA,

Location????

• Prokaryotic

Cyotoplasm and ribosomes

• Eukaryotic

Nucleus and ribosomes

DNA vs. RNA(players)DNA vs. RNA(players)

• DNA • Double Helix• Deoxyribose sugar• Adenine pairs with

Thymine (A-T)• Stays in nucleus

• RNA• Single strand• Ribose sugar• Uracil replaces

Thymine!• Leaves nucleus to

do the work

DNA vs. RNA

DNA RNADeoxyribose RibsoseThymine Uracil is one of the

bases in RNA. There is

thymine no thymine. This means

A goes with U and G still goes with C.

Double Strand Single Strand

Steps to Protein Synthesis1. Transcription – process where

DNA message is changed into mRNA then out of nucleus to the ribosomes!!!

2. Translation – process when mRNA is translated into amino acid chains(protein) on the ribosomes.

Transcription???

• Purpose?

• Creating?

• WHY WHY WHY!!!!!!

How does a protein get built??

• This is where RNA becomes involved.

• DNA is too large to get out of the nuclear membrane pores.

• SO RNA has to be made to go to the ribosomes!!!

SO, HOW DOES AN AMINO ACID CHAIN GET BUILT?

RNA stands for ribonucleic acid

Stars of Translation and Transcription

1. mRNA

2. DNA

3. rRNA

4. tRNA

5. Ribsomes

6. RNA polymerase

Three types of RNA:Three types of RNA:

• 1. mRNA• “messenger” RNA• Carries code for

proteins from DNA• Carries “codon”

• 2. tRNA• “transfer” RNA

• Attaches specific Amino Acids to the protein chain by matching the mRNA codon with the anticodon.

RNA TRANSCIPTIONThere are three (3) types RNA:1. Messanger RNA – (mRNA) carries messages from the DNA in the nucleus to the ribosomes.

tRNA2. Transfer RNA – (tRNA) 20 different

kinds which are only able to bond with one (1) specific type of amino acid.

rRNA3. Ribosomal RNA – (rRNA) major

component (part) of the ribosomes

3. 3. Ribosomal Ribosomal RNA - rRNARNA - rRNA• Where Protein

synthesis occurs

How Does RNA polymerase(complex) know where to start and stop?

• Promoter site: starting and stopping point on DNA. Specific base sequences that represents a gene.

• Termination site: Place where RNA polymerase stops!!!

• REMEMBER - only a gene is being read to make mRNA not all of your DNA.

Step 1: Step 1: • RNA polymerase complex attaches to DNA

at special places that serve as the start signal(promoter sites). Only one gene!!!!!

Step 2: Step 2: • DNA splits at site of RNA polymerase.

• RNA polymerase attaches matching bases to form new RNA strand from DNA template.

• RNA polymerase keeps adding bases making the RNA strand grow…

Step 3:Step 3:• RNA polymerase leaves DNA when reaches

the termination site(stop signal).

• RNA strand is released and goes to cytoplasm.

• DNA rewinds itself into the double helix.

Results of TranscriptionResults of Transcription

• Strand of mRNA made from the DNA

FYI

RNA polymerase doesn’t check for mistakes in the code. Doesn’t cause mutations when there is a few mistakes in proteins unlike replication.

Protein Synthesis: Protein Synthesis: TranscriptionTranscription

Making mature mRNA Original mRNA transcribed

is not mature mRNA

Exons: readable segments of mRNA that will be spliced together to make mature mRNA.

Introns: are non- readable segments of mRNA that must be removed before it leaves the nucleus

Exons vs. IntronsExons vs. Introns

Once introns removed, mRNA is ready to leave the nucleus!!!!

DNA

Cytoplasm

Nucleus

Eukaryotic Transcription

ExportG AAAAAA

RNA

Transcription

Nuclear pores

G AAAAAA

RNAProcessing

mRNA

Prokaryotic Protein Synthesis

• All occurs in the cyotplasm!!!

Transcription is done…what Transcription is done…what now?now?

Now we have mature mRNA transcribed from the cell’s DNA. It is leaving the nucleus through a nuclear pore. Once in the cytoplasm, it finds a ribosome so that translation can begin.

We know how mRNA is made, but how do we “read” the code?

Translation

Translation is the process of decoding a mRNA molecule into a polypeptide chain or protein.

ALWAYS read mRNA!!!!!!

Reading FrameReading Frame

• Every 3 DNA bases pairs with 3 mRNA bases

• Every group of 3 mRNA bases encodes a single amino acid

• Codon- coding triplet of mRNA bases

Codons

• Each combination of 3 nucleotides on mRNA is called a codon or three-letter code word.

• Each codon specifies a particular amino acid that is to be placed in the polypeptide chain (protein).

Protein Synthesis: Translation

Start codons and Stop codonsStart codons and Stop codons

• For translation to begin, there is a START codon.

• AUG: is the 3 letter codon that starts the process.

• UAA, UGA, UAG: Stop codons.

SU

GA

R-P

HO

SP

HA

TE

BA

CK

BO

NE

B A

S E

S

H

PO

O

HO

O

O

CH2NH2N

NH

N

N

HOH

P

O

O

HO

O

O

CH2

NH2

N

N

N

N

H

P

O

OH

HO

O

O

CH2

NH2

N

N

N

N

O

A Codon

GuanineGuanine

AdenineAdenine

AdenineAdenine

Arginine

Start Codon

• Start codon: codon AUG also serves as the “initiator” codon, which starts the synthesis of a protein.

Stop Codon

• STOP codon: Codon that signal the end of the protein. (UAA, UAG, & UGA

• Besides selecting the amino acid methionine, the codon AUG also serves as the “initiator” codon, which starts the synthesis of a protein


•A three-letter code is used because there are 20 different amino acids that are used to make proteins.

•If a two-letter code were used there would not be enough codons to select all 20 amino acids.

•That is, there are 4 bases in RNA, so 42 (4x 4)=16; where as 43 (4x4x4)=64.

Translation•Therefore, there is a total of 64 codons with mRNA, 61specify a particular amino acid.

• This means there are more than one codon for each of the 20 amino acids.

Protein Synthesis: TranslationTransfer RNA (tRNA)

•Each tRNA molecule has 2 important sites of attachment.

•One site, called the anticodon, binds to the codon on the mRNA molecule.

•The other site attaches to a particular amino acid.

•During protein synthesis, the anticodon of a tRNA molecule base pairs with the appropriate mRNA codon.

tRNAtRNA

• Transfer RNA• Bound to one amino

acid on one end• Anticodon on the

other end complements mRNA codon

MethionineMet-tRNA

U*

9

262223Pu

16

12Py 10

25

20:1

G*

17:1

Pu

A20:2

1713

20G

A5051

656463

G

62

52

CPu

59

A*

C

Py

T49

39

4142

31

2928

Pu*

43127

U35

38

36

Py*

34

403047:1

47:15

46

Py47:16

4544

47

73CCA

707172

66676869

321

7654

A CU

Anticodon

Parts of a RibosomesParts of a Ribosomes

• For translation to begin, 2 subunits of ribsosomes must unite, separate in cytoplasm – Large– Small

• Contain 3 binding sites – helps tRNA align to codon.– E– P– A

RNA TRANSLATIONProtein Synthesis: the formation of a protein using information coded on DNA and carried out by RNA in the assembly of amino acids.

Proteins are:a. Amino acids in chains – 20 kindsb. Made of 10’s or 100’s or 1000’s of amino acidsc. Must be arranged in a specific sequence for each

type of proteind. Function & type of protein is determined by amino

acid sequencee. DNA makes RNAf. RNA constructs amino acids

Steps of TranslationSteps of Translation• 1. INITIATION:

A.The initiator(start) codon AUG binds to the first anticodon of tRNA, signaling the start of a protein.

B. Two parts of the ribosome join around the tRNA and mRNA.

• The amino acid methionine, the codon AUG also serves as the “initiator” codon, which starts the synthesis of a protein

TranslationTranslation• 2. ELONGATION: The anticodon of

another tRNA binds to the next mRNA codon, bringing the 2nd amino acid to be placed in the protein. This will continue until stop codon.

• As each anticodon & codon bind together a peptide bond forms between the two amino acids.

Protein Synthesis: TranslationProtein Synthesis: Translation

3. Termination: The protein chain continues to grow until a stop codon reaches the ribosome, which results in the release of the new protein and mRNA, completing the process of translation. The amino acids are bonded with a peptide bond to form a protein.

•Release factor causes the release of tRNA and mRNA.

Summary of Translation• Ribosome 2 parts come together.• mRNA attaches to ribosome.• AUG – start codon. • tRNA brings in making anticodon with

amino acid.• rRNA continues to read mRNA and bring

in making tRNA.*Stop codon will stop process. Peptide

bonds will form to make a protein.

tRNA FunctiontRNA Function

• Amino acids must be in the correct order for the protein to function correctly

• tRNA lines up amino acids using mRNA code

Protein Synthesis: TranslationProtein Synthesis: TranslationTransfer RNA (tRNA)

•Each tRNA molecule has 2 important sites of attachment.

•One site, called the anticodon, binds to the codon on the mRNA molecule.

•The other site attaches to a particular amino acid.

•During protein synthesis, the anticodon of a tRNA molecule base pairs with the appropriate mRNA codon.

MethionineMet-tRNAMet-tRNA

U*

9

262223Pu

16

12Py 10

25

20:1

G*

17:1

Pu

A20:2

1713

20G

A5051

656463

G

62

52

CPu

59

A*

C

Py

T49

39

4142

31

2928

Pu*

43127

U35

38

36

Py*

34

403047:1

47:15

46

Py47:16

4544

47

73CCA

707172

66676869

321

7654

A CU

Anticodon

AE

Large subunit

P

Small subunit

Translation - InitiationTranslation - Initiation

fMet

UACGAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA

3’

AE

Ribosome P

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

Translation - ElongationTranslation - Elongation

GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA

3’

AE

Ribosome P

PheLeu

Met

SerGly

Polypeptide

Arg

Aminoacyl tRNA

UCUCCA



3’

AE

Ribosome P


Aminoacyl tRNA

CGA

Ala

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide


3’

AE

Ribosome P


CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

CGA

Ala


3’

Protein Synthesis: TranslationProtein Synthesis: Translation

The Genetic CodeThe Genetic Code

ACGATACCCTGACGAGCGTTAGCTATCGUGCUAUGGG ACUGProtein Synthesis: TranslationProtein Synthesis: Translation

ANYTHING

ACIDAMINE

Protein SynthesisProtein Synthesis

C

O

OHCN

H

HH

C

HO H

C

H

O

CN

H

HH

C

H H

C

H

O

OHCN

H

HH

C

HO H

Serine

C

H

O

OHCN

H

HH

C

H H

AlanineH

C

O

OHC

R

N

H

H

Amino Acid

H2O

3’

5’

5’

3’

Transcription And Translation Transcription And Translation In ProkaryotesIn Prokaryotes

Ribosome

Ribosome5’

mRNA

RNAPol.

Transcription vs. Translation ReviewTranscription vs. Translation Review

Transcription• Process by which

genetic information encoded in DNA is copied onto messenger RNA

• Occurs in the nucleus• DNA mRNA

Translation• Process by which

information encoded in mRNA is used to assemble a protein at a ribosome

• Occurs on a Ribosome• mRNA protein

ANYTHING

ACIDAMINE

Protein Synthesis

C

O

OHCN

H

HH

C

HO H

C

H

O

CN

H

HH

C

H H

C

H

O

OHCN

H

HH

C

HO H

Serine

C

H

O

OHCN

H

HH

C

H H

AlanineH

C

O

OHC

R

N

H

H

Amino Acid

H2O

AE

Ribosome P

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

Translation - Elongation


3’

Prokaryotic - Protein synthesis

• Location – cytoplasm

• At the same time.

• Eukaryotic – Protein synthesis

3’

5’

5’

3’

Transcription And Translation In Prokaryotes

Ribosome

Ribosome5’

mRNA

RNAPol.

(1961)(1961) Watson & Crick proposed… Watson & Crick proposed…• ……DNA controlled cell function by DNA controlled cell function by

serving as a template for serving as a template for PROTEINPROTEIN structure.structure.

• 3 Nucleotides = a triplet or 3 Nucleotides = a triplet or CODONCODON(which code for a specific AMINO ACID)(which code for a specific AMINO ACID)

See p.303See p.303

• AMINO ACIDSAMINO ACIDS are the building blocks are the building blocks of proteins.of proteins.

MUTATIONSChanges in DNA that affect genetic

information

Gene Mutations

• Point Mutations – changes in one nucleotides

1. Substitution – base is replaced• THE FAT CAT ATE THE RAT• THE FAT HAT ATE THE RAT

Gene Mutations2. Insertion – a base is added

• THE FAT CAT ATE THE RAT

• THE FAT HCA TAT ETH ERA T

H

Point Mutations that cause Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function.

3. Deletion – delete a base THE FAT CAT ATE THE RAT TEF ATC ATA TET GER AT

Effects of Mutations

• Silent – When a base pair is substituted but the change still codes for the same amino acid in sequence. NO CHANGE!!!

Effects 0f Mutations

• Missense –Mutation that causes a changed amino acid. Usually harmful!!!

• EX: sickle cell amenia

Effects of Mutations

• Nonsense – Mutation that does not allow protein to form because of early stop codon

Sex Chromosome Abnormalities

• XYY Syndrome– Normal male traits– Often tall and thin– Associated with antisocial and behavioral

problems

Chromosome Mutations• Changes in number and structure of entire

chromosomes

• Original Chromosome ABC * DEF

• Deletion AC * DEF

• Duplication ABBC * DEF

• Inversion AED * CBF

• Translocation ABC * JKL

GHI * DEF

Significance of Mutations• Most are neutral

• Eye color• Birth marks

• Some are harmful• Sickle Cell Anemia• Down Syndrome

• Some are beneficial• Sickle Cell Anemia to Malaria• Immunity to HIV

What Causes Mutations?

• There are two ways in which DNA can become mutated:– Mutations can be inherited.

• Parent to child

– Mutations can be acquired.• Environmental damage• Mistakes when DNA is copied

Chromosome Mutations

• Down Syndrome– Chromosome 21 does

not separate correctly.– They have 47

chromosomes in stead of 46.

– Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence.

Chromosome Mutations

• Cri-du-chat– Deletion of material on 5th

chromosome– Characterized by the cat-like

cry made by cri-du-chat babies

– Varied levels of metal handicaps

Sex Chromosome Abnormalities• Klinefelter’s Syndrome

–XXY, XXYY, XXXY

–Male

–Sterility

–Small testicles

–Breast enlargement

Sex Chromosome Abnormalities• XYY Syndrome

–Normal male traits–Often tall and thin–Associated with antisocial and

behavioral problems

Sex Chromosome Mutations

• Turner’s Syndrome– X– Female– sex organs don't

mature at adolescence– sterility– short stature

Sex Chromosome Mutations

• XXX

–Trisomy X

–Female

–Little or no visible differences

–tall stature

–learning disabilities

–limited fertility

Protein Synthesis DNA Transcription and Translation.

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