1. DNA, RNA structure 2. Transcription, translation

1. DNA, RNA structure

2. Transcription, translation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin

DNA is a double-stranded helix

Figure 10.3A, B


• DNA is a nucleic acid, made of long chains of nucleotides

DNA and RNA are polymers of nucleotides

Figure 10.2A

Nucleotide

Phosphate group

Nitrogenous base

Sugar

Polynucleotide Sugar-phosphate backbone

DNA nucleotide

Phosphategroup

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

Thymine (T)

Sugar(deoxyribose)


• DNA has four kinds of bases,

– Adenine(A), Thymine (T), Cytosine (C), and Guanine (G)

Figure 10.2B

Thymine (T) Cytosine (C) Adenine (A) Guanine (G)


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

– Anit-Parellel: means parellel but moving in different directions

Figure 10.5B

5 end 3 end

3 end 5 end

P

P

P

PP

P

P

P


• RNA is also a nucleic acid– different sugar (ribose)

– Uracil instead of Thymine

– Still has Adenine, Guanine, Cytosine

– Single strand, usually

Figure 10.2C, D

Phosphategroup

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

Uracil (U)

Sugar(ribose)


Types of RNA

Images: Blueprint, clipart; Factory, Andreas Praefcke; Truck, PRA.

Genetic information copied from DNA is transferred to 3 types of RNA:

__________ RNA: mRNA

Copy of information in DNA that is brought to the ribosome and translated into protein by tRNA & rRNA.

__________ RNA: rRNA

Most of the RNA in cells is associated with structures known as ribosomes, the protein factories of the cells.

It is the site of translation where genetic information brought by mRNA is translated into actual proteins.

___________ RNA: tRNA

Brings the amino acid to the ribosome that mRNA coded for.

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

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http://www.scienceprofonline.org/virtual-cell-main.html

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– The DNA is transcribed into RNA, which is translated into a chain of amino acids

– Bases of Central Dogma

Figure 10.6A

DNA

RNA

Protein

TRANSCRIPTION

TRANSLATION

• The information constituting an organism’s genotype is carried in its sequence of bases


Transcription produces mRNA

Figure 10.9A

RNApolymerase

RNA nucleotide

Direction oftranscription

Newly made RNA

Templatestrand of DNA


• In transcription, DNA helix unzips

– RNA nucleotides line up along one strand of DNA, following the base-pairing rules

– single-stranded messenger RNA peels away and DNA strands rejoin

RNA polymerase

DNA of gene

PromoterDNA Terminator

DNAInitiation

Elongation

Termination

Area shownin Figure 10.9A

GrowingRNA

RNApolymerase

Completed RNA

Figure 10.9B


RNA transcripts of DNA


• The “words” of the DNA “language” are triplets of bases called codons

– The codons in a gene specify the amino acid sequence of a protein

– In other words, codons are every 3 bases.

Translation of mRNA into amino acids


Figure 10.7

DNA molecule

Gene 1

Gene 2

Gene 3

DNA strand

TRANSCRIPTION

RNA

Protein

TRANSLATIONCodon

Amino acid


• An exercise in translating the genetic code

Figure 10.8B

Startcodon

RNA

Transcribed strand

StopcodonTranslation

Transcription

DNA

Polypeptide


• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a protein

• The process is aided by transfer RNAs

Transfer RNA molecules serve as interpreters during translation

Figure 10.11A

Hydrogen bond

Amino acid attachment site

RNA polynucleotide chain

Anticodon


• Each tRNA molecule has a triplet anti-codon on one end and an amino acid attachment site on the other

Figure 10.11B, C

Anticodon

Amino acidattachment site


Ribosomes build chains of amino acids

Figure 10.12A-C

Codons

tRNAmolecules

mRNA

Growingprotein

Largesubunit

Smallsubunit

mRNA

mRNAbindingsite

P site A site

P A

Growingprotein

tRNA

Next amino acidto be added toprotein


An initiation codon marks the start of an mRNA message

Figure 10.13A

End

Start of genetic message

AUG = methionine


• mRNA, a specific tRNA, and the ribosome subunits assemble during initiation

Figure 10.13B

1

Initiator tRNA

mRNA

Startcodon Small ribosomal

subunit

2

P site

Largeribosomalsubunit

A site


• The mRNA moves one codon at a time relative to the ribosome

– A tRNA pairs with each codon, adding an amino acid to the growing protein

– A STOP codon causes the mRNA-ribosome complex to fall apart

– This results in a chain of amino acids

• Amino Acid (AA) + AA + AA + AA…etc = Protein

How does translation happen?


Transcription

RNA

RNA polymerase

DNA


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Translation

tRNA

Ribosome mRNA

Lysine

Translation direction


Pause for Worksheet

Complete -Protein Synthesis Worksheet-Book Worksheet

ba

Red object = ?What molecules are present in this photo?

Table 14.2Types of RNA

Type of RNA Functions in Function

Messenger RNA(mRNA)

Nucleus, migratesto ribosomesin cytoplasm

Carries DNA sequenceinformation to ribosomes

Transfer RNA(tRNA)

Cytoplasm Provides linkage between mRNAand amino acids;transfers aminoacids to ribosomes

Ribosomal RNA(rRNA)

Cytoplasm Structural component of ribosomes


• The sequence of codons in DNA spells out the primary structure of a protein

– A chain of amino acids form proteins that cells and organisms use

Review: The flow of genetic information in the cell is DNARNAprotein


Overview

______________

Synthesis of RNA under the direction of DNA (mRNA).

______________

Actual synthesis of a polypeptide (protein) under the direction of mRNA.

Eukaryotic Cell

Diagram: Transcription & Translation, NIHFrom the Virtual Cell Biology Classroom on ScienceProfOnline.com


Complete-DNA Molecule & Replication

Pause for Worksheet


So how is DNA read to make Amino acids

• We use the Genetic Coding Chart

• Virtually all organisms share the same genetic code- the sequence is what is important


U C A G

U

C

A

G

GACU

GACU

GACU

GACU

UUUUUCUUAUUG

CUUCUCCUACUG

AUUAUCAUAAUG

GUUGUCGUAGUG

phe

leu

leu

ile

met (start)

val

UCUUCCUCAUCG

CCUCCCCCACCG

ACUACCACAACG

GCUGCCGCAGCG

ser

pro

thr

ala

UAUUACUAAUAG

CAUCACCAACAG

AAUAAC

AAGAAA

GAUGACGAAGAG

tyr

stopstop

his

gln

asn

lys

asp

glu

UGUUGCUGAUGG

CGUCGCCGACGG

AGUAGCAGAAGG

GGUGGCGGAGGG

cys

stoptrp

arg

ser

arg

gly

Firs

t B

ase

Third

Base

Second Base

This is another one


Before we begin

• In DNA

– A binds with T (like AT&T)

– C binds with G (like Cover Girl)

– RNA is the same BUT there is no T

• It is a U so A and U bind together


Step 1:

• Create a DNA sequence with 30 bases

– Must start with TAC

– Must end with ATT

– After that you are good to go with any bases


Step 2:

• Using your DNA, make a complimentary mRNA strand


Step 3:

• Using your mRNA strand

– Start at the beginning and circle every 3 codons


Step 4:

• Look at your first codon

– Match the first letter, second letter and third letter to the Genetic Coding Chart.

– Write the Amino Acid under the circled codon


Step 5:

• Continue until all codons are labeled with an amino acid

• Now you have a chain of Amino Acids

– Also called a PROTEIN


Example

DNA strand A – T – G – C – C – T – T – T – G

– T – A – C – G – G – A – A – A – C

mRNA strand A – U – G – C – C – U – U – U – G

1st codon A-U-G amino acid = methionine

2nd codon C-C-U amino acid = proline

3rd codon U-U-G amino acid = leucine

methionine proline leucine


Complete the 3 Genetic Coding Worksheets

Pause for Worksheet


Confused? Here are links to fun resources that further

explain genetic transcription & translation:

• Molecular Genetics: Transcription & Translation Main Page on the Virtual Cell Biology Classroom of Science Prof Online.

• “That Spells DNA” song by Jonathan Coulton.

• DNA Transcription step-through animation by John Kyrk.

• Transcribe & Translate a Gene, from University of Utah.

• DNA Transcription and Protein Assembly animated movie by RedAndBrownPaperBag.

• Genetic by Sonic Youth.

• Transcription and Translation animated movie from PBS production “DNA: The Secret of Life.

• “The Protein Synthesis Song” by MrsPurpleMonster18.

(You must be in PPT slideshow view to click on links.)

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

Documents

1. DNA, RNA structure 2. Transcription, translation