dna mrna transcription introduction the central dogma of molecular biology cell polypeptide...

DNA

mRNA

Transcription

Introduction

The Central Dogma of Molecular Biology

Cell

Polypeptide(protein)

TranslationRibosome

DOGMA?

This central dogma 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!

DOGMA!

Principle, idea, or statement that is considered to be absolutely true. Kind of like a theory!!!!! But Crick called it a DOGMA!!!

DNA ---- RNA ----- Proteins!!!!!!

Central Dogma of Biology

The flow of information in the cell starts at DNA,

How does DNA determine what you look like?

What is the purpose for What is the purpose for proteins?proteins?

• 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

DNA vs. RNADNA vs. RNA

• 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.

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 RNARNA

rRNArRNA• Where Protein

synthesis occurs

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

• Promoter site: starting 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 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 go to the

ribsome

Introns: nonreadable

Segments that must be removed before leaving

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!!!!!!

Three RNAs play the key roles!!

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

mRNA - Codons

• Read 3 bases at a time on the mRNA called 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

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 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.

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

Protein Synthesis: Translation

•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: Translation

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

• If they do not match then the tRNA is rejected!!!!

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

tRNA parts

Parts of a Ribosomes - rRNAParts of a Ribosomes - rRNA

Ribosomes are composed of 2 subunits separate in cytoplasm – Large– Small

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

– E– P– A

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 at site P.

TranslationTranslation• 2. ELONGATION: The anticodon of

another tRNA binds to the next mRNA codon at site A, 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.

http://staff.jccc.net/pdecell/proteinsynthesis/translation/steps.html

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.

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

Translation - ElongationTranslation - Elongation

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

3’

AE

Ribosome P

Translation - ElongationTranslation - Elongation

Aminoacyl tRNA

CGA

Ala

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

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

3’

AE

Ribosome P

Translation - ElongationTranslation - Elongation

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

CGA

Ala

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

3’

The Genetic CodeThe Genetic Code

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 In Transcription And Translation In Prokaryotes ALL IN CYTOPLASM!!!Prokaryotes ALL IN CYTOPLASM!!!

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

Pigment is produced in the petal cells of the plant as the result of a chemical reaction. A chemical reaction takes place in the cytoplasm of a cell in which a colorless molecule is changed to a different molecule that now absorbs light and reflects red light without assistance. This reaction would take place very slowly and not much pigment would be produced during the life of the plant. As with almost all chemical reactions inside cells, this reaction is catalyzed by an enzyme which speeds up the rate of the reaction hundreds of thousands of times. In the presence of the enzyme, enough pigment is produced to quickly turn the cells and petals of the flower red. Without the enzyme, the cells would essentially stay colorless. With the enzyme, the plant flowers can turn red. The red flower trait is thus the result of the activity of an enzyme.

http://www.bioinformatics.org/tutorial/1-1.html

How Is DNA Responsible for What you Look Like or How You Feel?

The DNA in each chromosome makes up many genes (as well as vast stretches of noncoding DNA(introns), the function of which is unknown). A gene is any given segment along the DNA that encodes instructions that allow a cell to produce a specific product - typically, a protein such as an enzyme - that initiates one specific action. There are between 50,000 and 100,000 genes. These PROTEINS determine everything about you. SO your DNA control this code and what you look like!!!! It determines the amino acid codes!!

MUTATIONSChanges in DNA that affect genetic

information

Gene Mutations

• Point Mutations – changes in one or a few nucleotides– Substitution

• THE FAT CAT ATE THE RAT• THE FAT HAT ATE THE RAT

– Insertion• THE FAT CAT ATE THE RAT• THE FAT CAT XLW ATE THE RAT

– Deletion• THE FAT CAT ATE THE RAT• THE FAT ATE THE RAT

Gene Mutations• Frameshift Mutations – shifts

the reading frame of the genetic message so that the protein may not be able to perform its function.– Insertion

• THE FAT CAT ATE THE RAT• THE FAT HCA TAT ETH ERA T

– Deletion• THE FAT CAT ATE THE RAT• TEF ATC ATA TET GER AT

H

H

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