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DNA & RNA- Nucleic Acids and Protein Synthesis . IB Biology Ch. 16: Campbell Ch. 5&6: Orange Book. Objectives. Describe the history behind the discovery of DNA and its function Outline the structure of a nucleotide Describe the structure of the DNA molecule

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dna rna nucleic acids and protein synthesis

DNA & RNA- Nucleic Acids and Protein Synthesis

IB Biology

Ch. 16: Campbell

Ch. 5&6: Orange Book

objectives
Objectives
  • Describe the history behind the discovery of DNA and its function
  • Outline the structure of a nucleotide
  • Describe the structure of the DNA molecule
  • Describe the process of DNA replication including the various enzymes and that it is a semi-conservative process.
introduction
Introduction
  • Your genetic endowment is the DNA you inherited from your parents.
  • Nucleic acids are unique in their ability to direct their own replication.
  • The resemblance of offspring to their parents depends on the precise replication of DNA and its transmission from one generation to the next.
  • Once T.H. Morgan’s group showed that units of heredity are located on chromosomes, the two constituents of chromosomes - proteins and DNA - were the candidates for the genetic material.
  • Until the 1940s, the great heterogeneity and specificity of function of proteins seemed to indicate that proteins were the genetic material.
  • However, this was not consistent with experiments with microorganisms, like bacteria and viruses.
discovery of dna
Discovery of DNA
  • 1868: Miescher first isolated deoxyribonucleic acid, or DNA, from cell nuclei
fredrick griffith 1928
Fredrick Griffith- 1928
  • First suggestion that about what genes are made of.
  • Worked with:

1) Two strains of Pneumococcus bacteria:

Smooth strain (S) Virulent (harmful)

Rough strain (R) Non-Virulent

2) Mice-were injected with these strains of bacteria and watched to see if the survived.

3) Four separate experiments were done:

-injected with rough strain (Lived)

-injected with smooth strain (Died)

-injected with smooth strain that was heat killed (Lived)

-injected with rough strain & heat killed smooth (????)

slide6

Mixture of heat-killed S cells and living R cells

EXPERIMENT

Living R cells (control)

Living S cells (control)

Heat-killed S cells (control)

RESULTS

Mouse dies

Mouse healthy

Mouse healthy

Mouse dies

Living S cells

griffith s conclusion
Griffith’s Conclusion
  • Somehow the heat killed smooth bacteria changed the rough cells to a virulent form.
  • These genetically converted strains were called “Transformations”
  • Something (a chemical) must have been transferred from the dead bacteria to the living cells which caused the transformation
  • Griffith called this chemical a “Transformation Principle”
next breakthrough came from the use of viruses
Next Breakthrough came from the use of Viruses
  • Viruses provided some of the earliest evidence that genes are made of DNA
  • Molecular biology studies how DNA serves as the molecular basis of heredity
  • Are only composed of DNA and a protein shell.

T2 Bacteriophage- a typical virus

slide9

Phage reproductive cycle

Phage attaches to bacterial cell.

Phage injects DNA.

Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble.

Cell lyses and releases new phages.

Figure 10.1C

photo of t2 viruses
Photo of T2 Viruses

Fig. 16-3

Phage head

Tail sheath

Tail fiber

DNA

100 nm

Bacterial

cell

hershey chase experiment 1952
Hershey-Chase Experiment- 1952
  • In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2
  • To determine the source of genetic material in the phage, they designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection
  • They concluded that the injected DNA of the phage provides the genetic information
slide12

Fig. 16-4-1

EXPERIMENT

Radioactive protein

Phage

Bacterial cell

DNA

Batch 1: radioactive sulfur (35S)

Radioactive DNA

Batch 2: radioactive phosphorus (32P)

slide13

Fig. 16-4-2

EXPERIMENT

Empty protein shell

Radioactive protein

Phage

Bacterial cell

DNA

Batch 1: radioactive sulfur (35S)

Phage DNA

Radioactive DNA

Batch 2: radioactive phosphorus (32P)

slide14

Fig. 16-4-3

EXPERIMENT

Empty protein shell

Radioactivity (phage protein) in liquid

Radioactive protein

Phage

Bacterial cell

DNA

Batch 1: radioactive sulfur (35S)

Phage DNA

Centrifuge

Pellet (bacterial cells and contents)

Radioactive DNA

Batch 2: radioactive phosphorus (32P)

Centrifuge

Radioactivity (phage DNA) in pellet

Pellet

video clip of hershey chase
Video Clip of Hershey-Chase
  • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#
erwin chargaff 1950
Erwin Chargaff- 1950

Already known- DNA is a polymer of nucleotides- nitrogen base, pentose sugar, and a phosphate group.

Chargaff noticed a ratio of the bases:

30.3% Adenine

30.3% Thymine

19.5% Guanine

19.9% Cytosine

So, for DNA, the amt. of A = T, and

The amt. of C= G (Chargaff’s Rules)

who discovered the shape of dna
Who Discovered the Shape of DNA?
  • James Watson and Francis Crick (1954) are credited with finally piecing together all the information previously gathered on the molecule of DNA. They established the structure as a double helix - like a ladder that is twisted. The two sides of the ladder are held together by hydrogen bonds.
how did they get to their conclusions
How did they get to their conclusions?
  • They built many models, always perplexed at how it fit together, until one day, when they wandered into the office of a fellow scientist, Dr. Rosalind Franklin.
slide19

Along with Dr. Maurice Wilkins, she had taken x-ray crystallography photos of DNA. They saw her photos and realized the great secret- that DNA was coiled like a spring. They then made their model and won the Nobel Prize in 1962.

Franklin’s famous photo of DNA

so what is dna deoxyribonucleic acid
So, What is DNA?Deoxyribonucleic Acid
  • blueprint of life (has the instructions for making an organism)
  • codes for your genes
  • made of repeating subunits called nucleotides
  • shape is the double helix (twisted ladder)
i structure of dna 3 parts
I. Structure of DNA- 3 parts:
  • Sugar- Deoxyribose
  • Phosphate Group
  • Nitrogen bases

The sugar and phosphates make up the "backbone" of the DNA molecule.

Nucleotide

slide22

DNA and RNA are polymers of Nucleotides

DNA is a nucleic acid, made of long chains of nucleotides- Sugar, phosphate, nitrogen base.

Phosphate group

Nitrogenous base

Nitrogenous base(A, G, C, or T)

Sugar

Phosphategroup

Nucleotide

Thymine (T)

Sugar(deoxyribose)

DNA nucleotide**

Figure 10.2A

Polynucleotide

Sugar-phosphate backbone

nitrogen bases
Nitrogen bases

Bases come in two types:

a. Purines (adenine and guanine- A&G)

b. Pyrimidines (thymine and cytosine- T&C).

base pairing chargaff s rules
Base Pairing- Chargaff’s Rules
  • Watson and Crick reasoned that the pairing was more specific, dictated by the base structures
  • They determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C)
  • The Watson-Crick model explains Chargaff’s rules: Adenine pairs to Thymine (A-T)Guanine pairs to Cytosine (G-C)**Very important- remember this!!!!
dna bonding
DNA Bonding

The two sides of the helix are held together by Hydrogen bonds (weak)

The sides of the DNA, the sugar and phosphate, are held together with covalent bonds.

slide28

Each strand of the double helix is oriented in the opposite direction

  • The ends are referred to as the 3’ and 5’ ends.

5 end

3 end

P

P

P

P

P

P

P

P

3 end

5 end

Figure 10.5B

slide29

Summary:

  • Chargaff ratio of nucleotide bases (A=T; C=G)
  • Watson & Crick (Wilkins, Franklin)
  • The Double Helix
  • √ nucleotides: nitrogenous base (thymine, adenine, cytosine, guanine); sugar deoxyribose; phosphate group
dna replication and repair
DNA Replication and Repair
  • The relationship between structure and function is manifest in the double helix
  • Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material
the basic principle base pairing to a template strand
The Basic Principle: Base Pairing to a Template Strand
  • Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
  • In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules
slide33

Fig. 16-9-1

A

T

C

G

T

A

A

T

C

G

(a) Parent molecule

slide34

Fig. 16-9-2

A

T

T

A

C

G

G

C

A

T

A

T

T

A

T

A

C

C

G

G

(b) Separation of strands

(a) Parent molecule

slide35

Fig. 16-9-3

A

T

A

T

A

T

A

T

C

G

C

G

C

G

C

G

A

T

A

T

A

A

T

T

T

A

T

A

T

T

A

A

C

C

G

C

G

C

G

G

(c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand

(b) Separation of strands

(a) Parent molecule

slide37

Watson and Crick’s semiconservative model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand

  • Competing models were the conservative model (the two parent strands rejoin) and the dispersive model (each strand is a mix of old and new)
dna replication a closer look
DNA Replication: A Closer Look
  • The copying of DNA is remarkable in its speed and accuracy
  • More than a dozen enzymes and other proteins participate in DNA replication
dna replication depends on specific base pairing
DNA replication depends on specific base pairing
  • In DNA replication, the strands separate
    • Enzymes use each strand as a template to assemble the new strands

Nucleosomes

Parental moleculeof DNA

Both parental strands serveas templates

Two identical daughtermolecules of DNA

antiparallel nature
Antiparallel nature
  • 5’ end corresponds to the Phosphate end
  • 3’ end corresponds to the –OH sugar
  • Replication runs in BOTH directions

• One strand runs 5’ to 3’ while the other runs 3’ to 5’

• Nucleotides are added on the 3’ end of the original strand.

  • The new DNA strand forms and grows in the 5’  3’ direction only
building new strands of dna
Building New Strands of DNA

5’ end

3’ end

5’ end

building new strands of dna1
Building New Strands of DNA
  • Each nucleotide is a triphosphate:

(GTP, TTP, CTP, and ATP)

  • Nucleotides only add to the 3’ end of the growing strand (never on the 5’ end)
  • Two phosphates are released (exergonic) and the energy released drives the polymerization process.
getting started
Getting Started
  • Replication begins at special sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble”
  • A eukaryotic chromosome may have hundreds or even thousands of origins of replication
  • Replication proceeds in both directions from each origin, until the entire molecule is copied
slide45

Fig. 16-12b

Origin of replication

Double-stranded DNA molecule

Parental (template) strand

Daughter (new) strand

0.25 µm

Replication fork

Bubble

Two daughter DNA molecules

(b) Origins of replication in eukaryotes

slide46

Fig. 16-12

Origin of replication

Parental (template) strand

Daughter (new) strand

Replication fork

Double-

stranded

DNA molecule

Replication bubble

0.5 µm

Two daughter DNA molecules

(a) Origins of replication in E. coli

Origin of replication

Double-stranded DNA molecule

Parental (template) strand

Daughter (new) strand

0.25 µm

Replication fork

Bubble

Two daughter DNA molecules

(b) Origins of replication in eukaryotes

getting started enzymes
Getting Started- Enzymes
  • At the end of each replication bubble is a replication fork, a Y-shaped region where new DNA strands are elongating
  • Topoisomerasecorrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
  • Helicasesare enzymes that untwist the double helix at the replication forks
  • Single-strand binding protein binds to and stabilizes single-stranded DNA until it can be used as a template
slide48

Fig. 16-13

Primase

Single-strand binding proteins

3

Topoisomerase

5

3

RNA primer

5

5

3

Helicase

slide49

DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the 3 end

  • The initial nucleotide strand is a short RNA primer
rna primers
RNA Primers
  • An enzyme called primase can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
  • The primer is short (5–10 nucleotides long), and the 3 end serves as the starting point for the new DNA strand.
synthesizing a new dna strand
Synthesizing a New DNA Strand
  • Enzymes called DNA polymerases catalyze the elongation of new DNA at a replication fork
  • Most DNA polymerases require a primer and a DNA template strand
  • The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells
slide52

3

DNA polymerasemolecule

5

How DNA daughter strands are synthesized

5 end

Daughter strandsynthesizedcontinuously

Parental DNA

5

3

Daughter strandsynthesizedin pieces

3

P

5

  • The daughter strands are identical to the parent molecule

5

P

3

DNA ligase

Overall direction of replication

Figure 10.5C

dna replication new strand development
DNA Replication-New strand Development
  • Leading strand: synthesis is toward the replication fork

(only in a 5’ to 3’ direction from the 3’ to 5’ master strand)

-Continuous

  • Lagging strand: synthesis is away from the replication fork

-Only short pieces are made called “Okazaki fragments”

- Okazaki fragments are 100 to 2000 nucleotides long

-Each piece requires a separate RNA primer

-DNA ligase joins the small segments together

(must wait for 3’ end to open; again in a 5’ to 3’ direction)

View video clip:

  • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#
slide56

Fig. 16-16a

Overview

Origin of replication

Leading strand

Lagging strand

Lagging strand

2

1

Leading strand

Overall directions of replication

key enzymes required for dna replication pg 314
Key Enzymes Required for DNA Replication (pg. 314)
  • Helicase - catalyzes the untwisting of the DNA at the replication fork
  • SSBP’s - single stranded binding proteins, prevents the double helix from reforming
  • Topoisomerase – Breaks the DNA strands and prevents excessive coiling
  • Primase – synthesizes the RNA primers and starts the replication first by laying down a few nucleotides initially.
  • **DNA Polymerase III - catalyzes the elongation of new DNA and adds new nucleotides on the 3’ end of the growing strand.
  • **DNA polymerase I- Replaces the RNA primers.
  • **Ligase- Connects the Okazaki fragments.
prokaryotic vs eukaryotic replication
Prokaryotic vs Eukaryotic Replication
  • Prokaryotes
    • Have one single, circular loop of DNA (no free ends)
    • Contains 4 x 106 base pairs (1.35 mm)
    • (e coli has 4.6 million base pairs)
    • Rate for replication: 500 nucleotides per second
    • Only one origination point
eukaryotic replication
Eukaryotic Replication
  • Eukaryotes w/Chromosomes:

-Have free ends

-Humans have approx. 3 billion base pairs = 1 meter

-Rate for replication: 50 per second (humans)

-Lagging strand is not completely replicated

-Small pieces of DNA are lost with every cell cycle

-End caps (Telomeres) protect and help to retain the genetic information

-Each chromosome is one DNA molecule

proofreading and repairing dna
Proofreading and Repairing DNA
  • Errors:
    • Rate is one every 10 billion nucleotides copied
    • Proofreading is achieved by DNA polymerase (pg. 318)
  • DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides
  • In mismatch repair of DNA, repair enzymes correct errors in base pairing
  • DNA can be damaged by chemicals, radioactive emissions, X-rays, UV light, and certain molecules (in cigarette smoke for example)
  • In nucleotide excision repair, a nucleasecuts out and replaces damaged stretches of DNA
proofreading and repairing dna1
Proofreading and Repairing DNA
  • Thymine dimer distorts the DNA molecule
  • A nuclease enzyme cuts the damaged DNA strand at two points and the damaged section is removed.
  • Repair synthesis by a DNA polymerase fills in the missing nucleotides.
  • DNA ligase seals the free end of the new DNA to the old DNA, making the strand complete.

Nuclease

DNA polymerase

DNA ligase

telomeres
Telomeres
  • Short, non-coding pieces of DNA
  • Contains repeated sequences (ie. TTGGGG 20 times)
  • Can lengthen with an enzyme called Telomerase
  • Lengthening telomeres will allow more replications to occur.
  • Telomerase is found in cells that have an unlimited number of cell cycles (commonly observed in cancer cells)
  • Artificially giving cells telomerase can induce cells to become cancerous
  • Shortening of these telomeres may contribute to cell aging and Apotosis (programmed cell death)

Ex. A 70 yr old person’s cells divide approx. 20-30X vs an infant which will divide 80-90X

slide63

Fig. 16-20

Telomeres

1 µm

a chromosome consists of a dna molecule packed together with proteins
A chromosome consists of a DNA molecule packed together with proteins
  • The bacterial chromosome is a double-stranded, circular DNA molecule associated with a small amount of protein
  • Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein
  • In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the nucleoid
chromatin packing in eukaryotes
Chromatin Packing In Eukaryotes
  • Chromatinis a complex of DNA and protein, and is found in the nucleus of eukaryotic cells
  • Histonesare proteins that are responsible for the first level of DNA packing in chromatin
  • Nucleosomes- are like beads on a string, consist of DNA wound twice around a protein core composed of two molecules each of the 4 main histone types.
slide66

Fig. 16-21a

Nucleosome

(10 nm in diameter)

DNA double helix (2 nm in diameter)

H1

Histone tail

Histones

DNA, the double helix

Histones

Nucleosomes, or “beads on a string” (10-nm fiber)

See p. 320

slide67

Fig. 16-21b

Chromatid

(700 nm)

30-nm fiber

Loops

Scaffold

300-nm fiber

Replicated chromosome (1,400 nm)

30-nm fiber

Looped domains (300-nm fiber)

Metaphase chromosome

part 2

Part 2

RNA and Protein Synthesis

Campbell: Ch. 17

i structure of rna 3 parts
I. Structure of RNA- 3 parts
  • Sugar- Ribose
  • Phosphate Group
  • Nitrogen-containing bases
    • Adenine
    • Uracil (substituted for Thymine)
    • Guanine
    • Cytosine

Also- RNA is single-stranded, unlike DNA.

- RNA is much smaller than DNA

- RNA is in the nucleus and cytoplasm

3 types of rna used to build proteins
3 Types of RNA (used to build proteins)
  • Messenger RNA (mRNA)- carries the instructions from DNA to the ribosomes.
  • Transfer RNA (tRNA)- carries message from mRNA to find the specific amino acids.
  • Ribosomal RNA (rRNA)- makes up ribosomes, it puts the proteins together.
b transcription the copying of information from dna to rna
B. Transcription- The copying of information from DNA to RNA

Flow of Information is:

DNA  RNA Proteins

-Occurs in the nucleus.

-RNA Polymerase is needed.

-adds nucleotides to the 3’ end only

The base-pair rule is followed during transcription, except, instead of pairing thymine with adenine, when creating an RNA strand, uracil is used

DNA Strand: 3’- T G C A T C A G A – 5’

RNA Strand: 5’ -A C G U A G U C U – 3’

slide73

Only one strand of DNA (the template strand) is transcribed. (Antisense strand )

The strand left un copied is the sense strand

RNA nucleotides are available in the region of the chromatin

(this process only occurs during Interphase)

slide74

RNA polymerase

Transcription begins on the area of DNA that contains the gene. Each gene has three regions:

1. Promoter- turns the gene on or off2. Coding region - has the information on how to construct the protein3. Termination sequence - signals the end of the gene

DNA of Gene

Promoter DNA

Terminator DNA

Initiation

Elongation

Termination

GrowingRNA

Completed RNA

RNA polymerase

slide75

RNA Polymerase is responsible for reading the gene, and building the mRNA strand.

**3 Steps: Initiation  Elongation  Termination

how it works step one initiation
How it Works: Step One- Initiation
  • RNA Polymerase binds to the “Promoter” region on the DNA (upstream about 25 nucleotides)
  • RNA Polymerase recognizes this region because of the TATA box (sequence) on the antisense strand.
elongation
Elongation
  • DNA is untwisted (hydrogen bonds are broken)
  • About 10 base pairs are exposed
  • Nucleotides are are added to the 3’ end of the growing mRNA molecule
  • Proceeds at a rate of: 60 nucleotides/sec
termination
Termination
  • Termination site is reached by RNA Polyermase
  • In Eukaryotes “AATAAA” is the signal
  • In Bacteria Translation can occur as it is released from the first transcription event
  • Final mRNA molecule is made consisting of “Coded” and “Non-coded” regions
modification of pre mrna
Modification of pre mRNA

RNA is stable after a few modification steps.

This mRNA is going into the cytoplasm where there are many enzymes which would be detrimental to the messenger.

Or

DON’T KILL THE MESSENGER!!!!!

so eukaryotic mrna is processed before leaving the nucleus
So, Eukaryotic mRNA is processed before leaving the nucleus

Exon

Intron

Exon

Intron

Exon

  • Noncoding segments called introns are spliced out
  • A cap and a tail are added to the ends

DNA

TranscriptionAddition of cap and tail

Cap

RNAtranscriptwith capand tail

Introns removed

Tail

Exons spliced together

mRNA

Coding sequence

NUCLEUS

CYTOPLASM

mrna structure
mRNA Structure
  • 1) 5’ cap: modified guanine; protection; recognition site for ribosomes
  • 2) 3’ tail: poly(A) tail (adenine); protection; recognition; transport
  • 3) RNA splicing: involves Introns & Exons
  • Exons (expressed sequences) retained
  • Introns (intervening sequences)

-These are spliced out / spliceosome, and the exons are kept.

slide85

Gene 1

Gene 3

DNA molecule

Gene 2

DNA strand

Transcription

RNA

Codon

Translation

Polypeptide

Amino acid

protein synthesis translation
Protein Synthesis- Translation
  • Occurs in the cytoplasm.
  • The genetic code is used to translate mRNA into proteins.
  • Proteins are polymers, made of polypeptides.
  • Each is made with a specific sequence of amino acids
codons
Codons
  • Each 3 bases of mRNA is called a codon, which translate to a single amino acid. (See codon chart).
  • AUG is the start codon. This tells the ribosome to start making proteins.
codon chart aug is the start codon
Codon Chart- AUG is the start codon

Test for Understanding: A DNA sequence has the following bases:

T A C - A G A - T T A - G G G - A T T What amino acids does it code for? (You'll need to use the codon chart)

rrna or ribosomal rna
rRNA or ribosomal RNA

Ribosomes are the sites where the cell assembles proteins according to genetic instructions

They consist of two parts, the large (50s) and small (30s) subunits, and are located either free floating in the cytoplasm or bound to the endoplasmic reticulum…

slide92
tRNA
  • Transfer RNA (tRNA) is basically cloverleaf-shaped.
  • tRNA carries the proper amino acid to the ribosome when the codons call for them.
  • At the top of the large loop are three bases, the anticodon, which is the complement of the codon
translation structure of a ribosome
Translation- Structure of a ribosome

rRNA- site of mRNA codon & tRNAanticodon coupling

P site

holds the tRNA carrying the growing polypeptide chain

A site

holds the tRNA carrying the next amino acid to be added to the chain

E site

discharged tRNA’s

ribosomes build polypeptides
Ribosomes Build Polypeptides

Next amino acidto be added topolypeptide

Growingpolypeptide

tRNA

molecules

P site

A site

Growingpolypeptide

Largesubunit

tRNA

P

A

mRNA

mRNAbindingsite

Codons

mRNA

Smallsubunit

Figure 10.12A-C

translation step 1 initiation
Translation- Step 1- Initiation
  • So here it goes:
  • In the first step in protein synthesis, the small subunit of the ribosome binds to the mRNA molecule at the start codon
  • The first tRNA delivers its amino acid
  • The larger unit of rRNA is also attached
2 elongation
2. Elongation
  • Begins when the next tRNA binds to the A site of the ribosome
  • The first tRNA is released after the amino acid is taken
  • The next  tRNA moves from the A site to the P site
  • and the used tRNA moves to the E site where it is released
  • This process continues until it reaches the stop codon.
3 termination
3. Termination
  • The ribosome reaches the stop codon.
  •   The polypeptide is released along with the two ribosomal units.
slide99

Amino acid

Polypeptide

Asite

P site

Anticodon

mRNA

1

Codon recognition

mRNAmovement

Stopcodon

Newpeptidebond

2

Peptide bond formation

3

Translocation

Figure 10.14

slide100

Newpeptidebondforming

Growing

polypeptide

Stage Elongation

4

A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time.

Codons

mRNA

Polypeptide

Stage Termination

5

The ribosome recognizes a stop codon. The poly-peptide is terminated and released.

Stop

Codon

Figure 10.15 (continued)

and so
And so,
  • DNA is copied into mRNA inside the nucleus.
  • The mRNA moves into the cytoplasm and tRNA and rRNA join up to read the message and produce a polypeptide chain
  • This will be further processed into a protein
summary
Summary

DNA Transcription RNA Translation Protein

DNARNA

Only 1 type 3 types

Deoxyribose ribose

A,C,G,T A,C,G,U

In nucleus in nucleus & cytoplasm

Made by replication made by transcription-mRNA

DNA codons RNA codons & anticodons

Relatively large Relatively small

Double-Stranded Single-Stranded

online animations
Online animations

Transcription to Translation**

http://207.207.4.198/pub/flash/26/transmenu_s.swf

Animated View of Transcription

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html#

Protein Synthesis (simple)

http://www.wisc-online.com/objects/index_tj.asp?objid=AP1302