From DNA to RNA Biology. Do you remember what proteins are made of ? Hundreds of Amino Acids link together to make one Protein There are 20 types of amino

From DNA to RNAFrom DNA to RNABiology

Do you remember what proteins are made of ?Do you remember what proteins are made of ?

• Hundreds of Amino Acids link together to make one Protein

• There are 20 types of amino acids, some we can make, and some we can’t

• There are infinite combinations of amino acids

• Can be hundreds or thousands monomers long. These long chains are called polypeptide chains

Protein SynthesisProtein Synthesis

• Protein synthesis is the process in which a cell makes protein based on the message contained within its DNA.

• However:• DNA is only found in the nucleus• Proteins are only made outside the nucleus – in

the cytoplasm.

Houston, we have a problem.

Protein SynthesisProtein Synthesis

• How do the many different messages within the DNA molecule get to the many ribosomes outside the nucleus?

• A molecular cousin of DNA – RNA – is used to carry these messages.

Before we talk about RNA, let’s review DNA (it’s been a while)

DNA - structureDNA - structureDNA – deoxyribonucleic acid

Shape – double helix

formed from 2 strands running in opposite directions

Composed of repeating nucleotides

Each nucleotide consists of

one sugar – deoxyribose

one phosphate – PO43-

one nitrogen base – adenine, guanine,

cytosine, or thymine

Nitrogen BasesNitrogen BasesPurines – composed of two rings

adenine(A)

guanine(G)

Pyrimidines – composed of one ring

thymine(T)

cytosine(C)

One purine and one pyrimidine hydrogen bond to join the two strands

adenine hydrogen bonds(2) with thymine

cytosine hydrogen bonds(3) with guanine

N H O CH3

N

N

O

N

N

N

N H

Sugar

Sugar

Adenine (A) Thymine (T)

N

N

N

N

Sugar

O H N

H

NH

N OH

H

N

Sugar

Guanine (G) Cytosine (C)Figure 16.8

H

The Double HelixThe Double Helix

NucleotidesNucleotides

Phosphate is on the “outside”

Sugar is in the “middle”

Base is in the “inside”

phosphate group

sugar (deoxyribose)

ADENINE (A)

base with a double-ring

structure

THYMINE (T)

base with a single-ring structure

CYTOSINE (C)

base with a single-ring structure

GUANINE (G)

base with a double-ring

structure

DNA StructureDNA Structure

deoxyribose phosphate

thymine adenine cytosine guanine

5’3’

3’ 5’

DNA ReplicationDNA Replication

The process of copying the DNA. Each strand acts as a template for building a new strand in replicationSemiconservative – each new DNA molecule consists of one new strand and

one old strand.

DNA ReplicationDNA Replication

Bases pairs of original DNA molecule

An enzyme called helicase cause the hydrogen bonds to break & DNA begins to “unzip”

Free DNA nucleotides are paired with bases from the original strand. DNA Polymerase bonds the free nucleotides to the original strands

The result is 2 identical molecules of DNA – each with one new strand and one old strand

5’

5’

3’

3’

5’

3’ 5’

3’

Ribonucleic Acids (RNA)Ribonucleic Acids (RNA)

RNA is almost exactly like DNA, except:• Contains a ribose sugar, instead of a

deoxyribose sugar (hence the name…)• Contains uracil instead of thymine.• RNA is single-stranded, not double-

stranded (usually…)

Ribonucleic Acids (RNA)Ribonucleic Acids (RNA)

RNA• The job of RNA (ribonucleic acid) is to carry

messages from the DNA (in the nucleus) to the ribosomes (in the cytoplasm).

• RNA Consists of only one strand of nucleotides.– Nucleotides – one sugar(ribose), one

phosphate, and one nitrogen base• Nitrogen bases = adenine, uracil, cytosine,

and guanine.

3 Types of RNA

1.Messenger RNA (mRNA) – carries a message from the DNA to the cytoplasm

2.Transport RNA (tRNA) – transports amino acids to the mRNA to make a protein

3.Ribosomal RNA (rRNA) – make up ribosomes, which make protein.

Protein Synthesis OVERVIEWProtein Synthesis OVERVIEW

Occurs in TWO steps:1.Transcription – the genetic information

from a strand of DNA is copied into a strand of mRNA

2.Translation – the mRNA, with the help of the ribosome, forms a chain of amino acids (eventually forming a protein) based on the information contained on the mRNA.

The Central Dogma:The Central Dogma:

This order of events is called the central dogma of molecular biology:

Step One: TranscriptionStep One: Transcription

1. DNA unzips: enzymes split apart base pairs and unwind the DNA double helix.

2. Bases pair up: Free nucleotides in the cell find their complementary bases along the new strands with the help of RNA polymerase. What will be different??

3. New backbone formed: The sugar-phosphate backbone is assembled to complete the RNA strand, and separates from the DNA strand.

Protein Synthesis Transcription

Enzyme unzips DNA Free RNA nucleotides

bond with one side of DNA strand

RNA polymerase bonds the RNA nucleotides together.

mRNA leaves the nucleus for the cytoplasm

A

T

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Enzyme unzips DNA Free RNA nucleotides bond

with one side of DNA strand RNA polymerase bonds the

RNA nucleotides together. mRNA leaves the nucleus for

the cytoplasm DNA strands are rebonded

A

T

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C

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A


Watch this simplified animation:

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

Watch the more complex animation!

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html






Try it! What RNA strand will be made from the following DNA sequence?

TACGCATGACTAGCAAGTCTAACTAUGCGUACUGAUCGUUCAGAUUGA

Protein SynthesisTranslation

Involves all three types of RNA Ribosome(with rRNA) attaches to mRNA Ribosome locates the start codon “AUG” on the mRNA. On each tRNA is a “anticodon” that matches each codon tRNA “carries” or “transfers” the amino acids to the ribosome

as the ribosome “reads” the 3-letter codon in the mRNA. As each tRNA lines up according to the sequence of codons,

peptide bonds form between the amino acids.

Step Two: TranslationStep Two: Translation

1. So how exactly do you go about determining what protein your cells are going to make?

2. FIRST, Divide the mRNA sequence into codons. As you just saw and heard, codons are three-base sections of mRNA:

AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA


2. Since each 3-letter combination “codes” for an amino acid, you need to figure out what amino acid matches up with each codon:


?


The Genetic CodeThe Genetic Code




met ?







STOP

Translation

U A U G G C A U A U U A G

U A C

met

C G U

ala

A U A

isol

Translation


U A C

met

C G U

ala

A U A

isol

Translation


U A C

met

C G U

ala

A U A

isol

Translation


U A C

met

C G U

ala

A U A

isol

Translation


U A C

met

C G U

ala

A U A

isol

Translation


U A C

met

C G U

ala

A U A

isol

Translation


U A C

met

C G U

ala

A U A

isol

Translation


met

C G U

ala

A U A

isol

Translation


met

C G U

ala

A U A

isol

Translation


met ala

A U A

isol

A U C

stop

Translation


met ala

A U A

isol

A U C

stop

Translation


met ala

A U A

isol

A U C

stop

Translation


met ala

A U A

isol

A U C

stop

Translation


met ala

A U A

isol

A U C

stop

Translation


met ala

A U A

isol

A U C

stop

Translation


met ala isol

A U C

stop Protein Assembled


Watch this simplified animation:http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

Watch the more complex animation!http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf



Protein Synthesis WorksheetProtein Synthesis Worksheet

Copy the 7 steps from the top of the worksheet into your notes.

Protein Synthesis WorksheetProtein Synthesis WorksheetC C G C A U G C A C A C C G G A C C A U A G C G C U A U

C C G C A U G C A C A C C G A C C A U A G C G C U A U

C C G C A U G C A C A C C G A G A C C A U A G C G C U A U







Start His Thre Gly Pro STOP

Start His Thre Asp His Ser

Start His Thre Asp Thr Iso

Ala

Ala

RECAP:RECAP:

1. DNA is transcribed into mRNA in the nucleus.

2. The mRNA leaves the nucleus and enters the cytoplasm.

3. The protein is translated from the mRNA sequence using tRNA and amino acids.

Works CitedWorks Cited

Mr. Armfield

Sci. Dept.

Deerfield High School, Deerfield IL

Documents

From DNA to RNA Biology. Do you remember what proteins are made of ? Hundreds of Amino Acids link together to make one Protein There are 20 types of amino