dna (deoxyribonucleic acid)

DNA(Deoxyribonucleic Acid)

What is it? Read Chap 13

How does it work? Read Chap 14

How do we know? Read 13, 14 & class notes

The Central DogmaDNA makes PROTEINS and PROTEINS make LIFE

The Central DogmaDNA makes PROTEINS and PROTEINS make LIFE

But how? At its essence, DNA is a set of instructions

for making proteins. “DNA is a cookbook and the genes are recipes”

Proteins are made from different arrangements of protein building blocks called Amino Acids.

There are 20 different Amino Acids. You get them from your food.

So how do you change the protein in a tuna fish sandwich into human hemoglobin, hair, enzymes, etc.???

There’s a little problem here…

Step 1: Transcription Copying the DNA

DNA g mRNA

Transcription: Copying the DNADNAgmRNA

Transcription: Copying the DNADNAgmRNA

COMPARISON OF DNA AND MESSENGER RNA

Transcription: Copying the DNADNAgmRNA

COMPARISON OF DNA AND MESSENGER RNA

DNA mRNA

StructureDoubleHelix

SingleStrand

SugarDeoxyribose

C5 H10 O4

RiboseC5 H10 O5

Bases A,G,C,T A,G,C,UUracil

How can 4 bases tell you how to make proteins from 20 amino acids???

Law of Parsimony (The simplest answer is often the right answer. Sort of, not always but a lot.)

4 letter alphabet making 1–letter words?

4-letter alphabet making 2-letter words?

A G C T

AA GA CA TA

AG GG CG TG

AC GC CC TC

AT GT CT TT

mRNA & Codons

The 3-base units of information on mRNA are called codons.

AAU,GCC,CAU,GGG,CGA…………….

Codons “spell out” the names of the specific amino acids to be used in making a specific PROTEIN.

The sequence of bases on DNA or RNA is called, duh,

the “base sequence”

The Universal Genetic Code is 64 tripletsIt’s a 4-letter alphabet that makes 64 3-letter words

Protein Synthesis (makin’ proteins)So this movie requires another actor… TRANSFER RNA (tRNA)

Transfer RNA (tRNA)

Protein Synthesis

Some terms that you MUST know…

DNA codes or triplets (the genetic code of DNA)

TRANSCRIPTION (of DNA to make mRNA)

mRNA CODONS (3-base information units of mRNA

tRNA ANTICODONS (anticodons pair with codons)

TRANSLATION (tRNA reads mRNA to make a protein)

OK, so you want to make some protein…

Hook together AMINO ACIDS

with PEPTIDE BONDS

Protein Synthesis = Translation(makin’ proteins)

Codons

Transfer RNA (tRNA)“Picks up and transfers the amino acids over to the ribosome and mRNA”

codon in mRNA

anticodon in tRNA

amino

acid

Fig. 14-7, p.223

tRNA Structure

Protein Synthesis (makin’ proteins)

“Poly-ribosomes”

Overview

Transcription

Translation

mRNA rRNA tRNA

Mature mRNA transcripts ribosomal subunits mature tRNA

binding site for mRNA

P (first binding

site for tRNA)

A (second binding

site for tRNA)

initiation

elongation

Amino

Acid

1

Amino

Acid

2

Amino

Acid

1

Amino

Acid

2

a A mature mRNA transcript leaves the

nucleus through a pore in the nuclear

envelope.

c Initiation ends when a large and small ribosomal subunit converge and bind

together.

b Initiation, the first stage of translating mRNA, will start when an

initiator tRNA binds to a small ribosomal subunit.

d The initiator tRNA binds to the

ribosome.

e One of the rRNA molecules

Fig. 14-9a-e, p.224

f The first tRNA is released

g A third tRNA binds with the next

codon h Steps f and g are repeated

termination

i A STOP codon moves into the area where the

chain is being built.

j The new polypeptide chain is released from

the ribosome.

k The two ribosomal subunits now

separate, also.

Fig. 14-9f-k, p.224

and all this requires just 28 molecules…

20

5

2

1

THE END. TEST NEXT TIME.

Extra slides below.

Disregard the remaining slides…

Hershey

and

Chase

REPLICATION OF DNA