Protein Synthesis: Protein Synthesis: Part 1 (Transcription)Part 1 (Transcription)

Protein Synthesis: Protein Synthesis: Part 1 (Transcription)Part 1 (Transcription)

Ch 11Ch 11

Protein Synthesis means

Synthesizing Proteinsor

“MAKING” PROTEINS

learn how proteins are made.

The GOAL is to:

Protein Synthesis

can be broken down into two stages:

• Transcription• Translation

DNA mRNA Proteins

TRANSCRIPTION TRANSLATION

1st PROCESS 2nd PROCESS

1 2 3

Transcription

Reads and copies a section of DNA (AKA gene) and converts it into mRNA(A gene codes for a protein)

Let’s compare

DNA and RNA

DNA RNA

Sugar = deoxyribose

Sugar = ribose

Double helix (2 strands)

Single strand

DNA RNALocation: nucleus

Location:

Nucleus & cytoplasmBases:

A, C, G, TBases:

A, C, G, U (Uracil)

DNA RNA

Function: simply stores genetic info

(instructions to make proteins)

Function: many functions, all used to assemble proteins

Three types of RNA

• MESSENGER RNA (mRNA)

• TRANSFER RNA (tRNA)

• RIBOSOMAL RNA (rRNA)

MESSENGER RNA

• “mRNA”

• single strand

• contains genetic info

• is transported out of nucleus

TRANSFER RNA

• “tRNA”

• single strand

• folded like a hairpin

• binds specific amino acids

RIBOSOMAL RNA

• “rRNA”

• single strand

• found in ribosomes

• ribosomes are made up two pieces of rRNA

Let’s look at

TRANSCRIPTION

“The first process”

DOUBLE HELIX SPREADS APART

RNA POLYMERASE copies the gene by attaching RNA nucleotides

The product is called mRNA m

RN

A

Here the DNA is split open and a

mRNA strand is being made

Here the DNA is split open and a

mRNA strand is being made

NOTICE:

RNA POLYMERASE ADDS ON RNA NUCLEOTIDES TO MAKE mRNA

Then the newly constructed mRNA undergoes “processing”

mR

NA

The mRNA then leaves the nucleus to enter the next process “translation”

mRNA

T

A

C

T

G

A

T

A

T

C

DNAA

T

G

A

C

T

A

T

A

G

DNAA

U

G

A

C

U

A

U

A

G

RNA3’

5’ 3’

5’“start”

sequence

(Signals where to begin)

“terminator” sequence

(where to end)

RNA processing includes• cutting out meaningless DNA (aka introns)

• Adding a cap on the tip (aka GTP cap)

• Adding on A-A-A-A on the end (aka Poly-A tail)

Intron Intron Intron

+

=

Introns contain meaningless

DNA

Only the important, USEFUL DNA

Add on a GTP cap

Tack on a poly-A tail

mRNAGTP A-A-A

You are finished processing the mRNA. It can now leave the nucleus.

Describe what is happening here and who is involved

Translation• The process of converting the

mRNA codons into a sequence of amino acids to build a protein.

• A codon is a group of three nucleotides. Each codon codes for one amino acid.

Translation – using mRNA to bring the correct tRNA anticodon, with an amino acid attached. Occurs at the ribosome..

Translation Sequence

• A ribosome attaches to the “start” of the mRNA. The codon “AUG” signals the start.

• The tRNA having the anticodon “UAC” will bring the first amino acid to the ribosome to begin the formation of the protein.

• The ribosome slides to the next codon on the mRNA. The complementary tRNA anticodon brings the second amino acid to the protein strand.

• This process continues until the ribosome reaches a “stop” signal.

• Stop codons on mRNA are– UAA– UAG– UGA

A Protein has been made!

Mistakes Happen – Mutations!

A point mutation occurs when a single base pair is mismatched.

Ex. THE DOG BIT THE CAT THE DOG BIT THE CARA frameshift mutation occurs when

a single base is added or deleted.Ex. THE DOG BIT THE CAT THE OGB ITT HEC AT (the D was deleted)

• Which do you think would be more harmful? Why?