Protein Synthesis

Transcription and Translation

Protein Synthesis

Is the formation of the proteins using information coded on DNA and carried out by RNA

STEP 1 RNA Transcription STEP 2 RNA Translation DNA RNA Proteins

Protein

Each protein molecule is made up of one or more polypeptides.

Each polypeptide is made up of a sequence of amino acids.

There are 20 different types of Amino Acids.

Amino Acids Polypeptides Proteins

Genetic Code

System that contains information needed for proper cell functioning.

This information is built into the arrangement of nitrogen bases.

Codon

A specific group of three sequential bases on mRNA.

Each codon codes for a specific amino acid. There are 64 possible codons. Coding for amino acids is universal for all animals.

See Codon chart on Page 207 What does the following mRNA code for?

AUG UUU CCU CAA GGU GAG GCG ACA UAA

Transcription

First step in protein synthesis Occurs in the nucleus End result is RNA molecule with a

complementary base sequence to DNA.

Flow of Genetic InformationDNA RNA

RNA TRANSCRIPTION STEP 1

Enzyme called RNA Polymerase binds to DNA molecule at the promoter

Promoter is a sequence of nucleotides on a DNA molecule where transcription will begin

Once RNA polymerase binds to the DNA molecule it will unwind and separate the two complementary DNA strands.

RNA TRANSCRIPTIONSTEP 2

RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one of the DNA strands.

They will attach by hydrogen bonds and form a strand on messenger RNA.

RNA polymerase will also establish the sugar to phosphate bonds between the nucleotides in the new mRNA strand.

As the RNA Polymerase passes the separated DNA strands rewind.

RNA TRANSCRIPTIONSTEP 3

The enzyme will reach a pattern of bases on the DNA strand that signals termination.

The enzyme will stop and release the new

RNA strand.

The new RNA strand now moves to the cytoplasm

End Result of Transcription

Transcription just created a RNA molecule with a complementary base sequence to DNA.

Each type of RNA molecule (tRNA, mRNA, rRNA) is made this way and will start their job in protein synthesis.

RNA TRANSCRIPTION PRACTICE PROBLEM:

Transcribe a mRNA molecule from the following DNA Strands.

DNA: TAC ATA TAA CGC CCG AGC TGC GGC

Warm Up:

Transcribe a mRNA molecule from the following DNA Strands.

AGG TTA GGC CCG ATA AGC GCG GGC

Today:

Homework:

TRANSLATION

The process of assembling protein molecules from information encoded in mRNA.

Second Step in Protein Synthesis This process uses all three types of

RNA Process occurs in the cytoplasm

Transfer RNA (tRNA)

Transfer RNA (tRNA) bears a sequence of three bases called the Anticodon.

The anticodon base sequence is complimentary to the codon on the mRNA

tRNA carries an amino acid to the ribosome's

mRNA and tRNA will pair together during translation.

Translation- STEP 1 INITIATION

Process starts when mRNA migrates out of nucleus by nuclear pores, and migrates to the ribosome's.

Amino acids floating freely in the cytoplasm are transported to the ribosome's by the tRNA

STEP 1 INITIATION (CONT)

The assembly of polypeptides start when the ribosome's attaches to the AUG(start) codon of the mRNA

The AUG codon pairs with the anticodon UAC on a specific tRNA

Methionine is usually the first amino acid (not always the first in the amino acid chain because it may be removed)

STEP 2 & 3 ELONGATION

The Polypeptide chain is put together.

Ribosome's moves along the chain and decodes the mRNA and attaches the amino acids together by peptide bonds.

The tRNA will bring in the next amino acid,

pair up with the codon on the mRNA and attach the next amino acid together

STEP 4 TERMINATION

Eventually the ribosome reaches a stop codon and the process comes to the end

The new polypeptide is complete and released.

Ribosome's may be working at different parts of the mRNA simultaneously.

STEP 5 DISASSEMBLY

The components of translation separate.

The last tRNA leaves.

The Ribosome leaves the mRNA

The translation machinery are now ready to translate another mRNA

Translation Practice

DNA: TAC ATA TAA CGC CCG AGC TGC GGC

mRNA:

Amino Acid Chain: