SNC 4UDATE: ________________________

Translation

Translation Overview

Synthesis of proteins in the cytoplasm

Involves the following:

1.mRNA (codons)

2.tRNA (anticodons)

3.ribosomes

4.amino acids

Messenger RNA (mRNA)

_______________ the information for a specific protein

Made up of __________ to __________ nucleotides long

Sequence of 3 bases called codon

______ methionine or ___________________

__________________________ _________________

Transfer RNA (tRNA)

Made up of 75 to 80 nucleotides long; single stranded

Role _________________________________________________

At one end, picks up the appropriate _______________ floating in the cytoplasm

At the other end, has ________________ that are _______________________ to mRNA codons

Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds

E.g. if mRNA codon is AUA, anticodon is _______ and carries __________________

The Wobble Hypothesis

The _______________ in each codon may differ between two codons that code for the same amino acid

E.g. UAU and UAC both code for _________________

The tRNA with anticodon AUA can still bond to ________

Flexibility helps with possible errors made during _________________________

The Ribosome

Made of a ________ and __________ subunit

Composed of _______ (40%) and ____________ (60%)

Bind to mRNA at _________

_________________ of translation

Have two sites for tRNA attachment

P ___________________

A ___________________

move along mRNA in ___________ direction

_____________ is added each time a ribosome reads a codon

Reading frame

The phase in which to read the mRNA as groups of three

Possible problem

If ribosome doesnt start reading at the appropriate nucleotide, it could affect the polypeptide sequence

E.g. AUGCCAGAU... can have the following reading frames:

AUG CCA GAU... or UGC CAG AU...

It depends on where the ____________ begins ________________

Therefore, it is important that the mRNA be positioned properly

Translation

Three steps:

1. initiation: start codon (AUG)

2. elongation: amino acids linked

3. termination: stop codon (UAG, UAA, or UGA)

Initiation

Start codon (_______) is recognized by ribosome

Ensures correct reading frame

AUG codes for __________________

tRNA carrying methionine enters _________ (official initiation)

Elongation

The next ______ carrying the appropriate amino acid enters the _____

First amino acid bonds to second amino acid via _____________

Ribosome shifts (translocates) one ______________

tRNA in P site _____________ and is recycled

Now tRNA that was attached to A site is moved to ____________

3rd amino acid enters the now available ____________ and bonds to 2nd amino acid via peptide bond

Process continues until _______________ is reached

Termination

Ribosome reaches ____________________ (UGA, UAG, UAA)

Dont code for a.a., so no incoming tRNAs; process stops

Release factor

Recognizes process stopping

Aids in ___________ of ____________________________ from ribosome

Two ribosome subunits fall off mRNA; translation officially finished

____________________________ of protein is made

Homework

Page 254 # 1a-c, 2-4, 6, 7, 9

53

mRNA

A

U

G

C

U

A

C

U

U

C

G

1

-

tRNA

2

-

tRNA

U

A

C

G

aa1

aa2

A

U

A

peptide bond

3

-

tRNA

G

A

A

aa3

Ribosomes move over one codon

(leaves)

53

mRNA

A

U

G

C

U

A

C

U

U

C

G

1-tRNA

2-tRNA

U

A

C

G

aa1

aa2

A

U

A

peptide bond

3-tRNA

G

A

A

aa3

Ribosomes move over one codon

(leaves)

53

59

mRNA

A

C

A

U

G

U

aa1

aa2

U

primary

structure

of a protein

aa3

200

-

tRNA

aa4

U

A

G

aa5

C

U

aa200

aa199

terminator

or stop

codon

Termination

59

mRNA

A

C

A

U

G

U

aa1

aa2

U

primary

structure

of a protein

aa3

200-tRNA

aa4

U

A

G

aa5

C

U

aa200

aa199

terminator

or stop

codon

Termination

59