From DNA to Protein

True Purpose of Genetic Material –

Central Dogma

A. Overview DNA, as genetic blueprint of life, dictates

how to make every living thing Every cell’s job is to produce protein

› Why protein? Animals: enzymes, membranes,

organelles, muscle, skin, hair = protein Plants: enzymes, membranes, organelles

= protein Life = protein!

Making protein is cell’s doctrine or dogma› Central dogma: steps necessary to produce

protein Step 1: DNA transcribed to RNA Step 2: RNA translated to protein

B. Transcription (txn) Double-stranded (ds) DNA found in nucleus

of eukaryotes (cytoplasm of prokaryotes) Code of bases (A-C-G-T) on DNA

determines what type of protein synthesized in cytoplasm› Problem: DNA trapped in nucleus, can’t

leave› Solution: use different nucleic acid that’s

able to leave nucleus = single-stranded (ss) RNA!

Steps of Txn (nucleus) Step 1: RNA polymerase binds to DNA Step 2: RNA polymerase unwinds &

unzips DNA Step 3: RNA polymerase adds

complementary RNA bases to DNA› All bases are same as DNA except RNA

uses uracil instead of thymine

DNA: A T C C A G G T C A T G C A A G C

RNA:RNA: U A G G U C C A G U A C G U

U C G

DNA vs.

RNA

DNA

RNA

PO4

Nucleic acid

adenine

cytosine

guanine

Single-

strand

uracil

ribose

double-

strand

Deoxy-

ribose

thymine

Txn can occur at different DNA forks (just like replication)› Different segments of

DNA called “genes” that code for different proteins/items

T A C G A T T A C A G C A

Gene 1

C. RNA Three types of RNA made

depending on work needed1.Messenger RNA (mRNA)

brings information from DNA in nucleus to outside cytoplasm

2.Ribosomal RNA (rRNA) Contains ribosome that clamps onto mRNA put amino acids in right order

3.Transfer RNA (tRNA) carries amino acids to rRNA for assembly

D. Translation (trl) Act of making protein from mRNA

› Recall: amino acids are building blocks of proteins

mRNA sequence is “read”› Nucleotide sequence codes for 20 different

types of amino acids› Group of 3 nucleotides (triplet or codon)

codes for 1 amino acid Ex: UUU codes for phenylalanine

UAC codes for tyrosine

mRNA Codes Ex: AAC= asparagine

Let’s practice:

Step 1: put blocks around every 3 bases (1 codon)

Step 2: look up letters in mRNA code Step 3: write down amino acid sequence

AAACCUAAGGCCAACCUAAGGACC

lysine- proline- lysine- alanine - asparagine

- arginine - threonine

- leucine

Trl has repetition to compensate for possible mistakes & codes to start & stop› Repetition: proline is coded for by CCU, CCC,

and CCA› Start: codon AUG is where tln starts

(methionine)› Stop: codons UGA, UAA, UAG where trl stops

› Try it again! Do NOT start boxing codons until see START

codon “AUG” Stop translating when see STOP codon (UGA,

UAA, or UAG)

AACCAUGAAGGCCAACCUAUAGGACCG

Protein = methionine–lysine-alanine-asparagine-leucine

Translation

Steps of Trl

1. DNA undergoes txn to make mRNA in nucleus

2. mRNA leaves nucleus, enters cytoplasm & travels to ribosome (solo or on roughER)

3. tRNA binds to amino acids in cytoplasm based on anticodon & transports them to ribosome

4. ribosome bonds codon in mRNA to anticodons in tRNA, binding amino acids in right order until reaches STOP codon

Step 1: Txn in Nucleus

dsDNAmRNA

tRNA

ribosome

amino acid

Step 2: mRNA ribsome

dsDNAmRNA

mRNA

Step 3a: tRNA binds aa

dsDNAmRNA

Step 3b: tRNA/aa to ribosome

dsDNAmRNA

mRNAtRNA

try

ACC

Amino acid

anticodon

Ribosome

tRNA

CUA

met

tRNA

UA

his

G

Step 4a: tRNA/aa to mRNA

GAU GAUUGAAU GCmRNA

tRNA

A

try

C

Ribosome

(rRNA)

GAU GAUUGAAU GCmRNA

tRNA

CUA

met

his

tRNA

UAG

tRNA

A

try

C C

Step 4b: aa join as protein