Control, Genomes and Environment

Cellular Control – Translation, RNA and cAMP

Keyword recap1. Transcription A. Each amino acid can be coded for by

more than one codon (*)

2. Ribosome B. The creation of a double stranded DNA copy of a DNA molecule

3. RNA C. The creation of a single stranded mRNA copy of the DNA coding strand

4. codon D. The single stranded copy of the template strand, contains U instead of T

5. mRNA E. Organelle found in the cytoplasm of cells. Required for the synthesis of proteins

6. RNA polymerase

F. A triplet of nucleotide bases

7. Degenerate G. Ribonucleic acid

8. replication H. An enzyme which binds to DNA to catalyse the joining of free nucleotides to the DNA template strand

* Which are the exception to this rule?

Learning Outcomes

• describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes

• State that cAMP activates proteins by altering their 3D structure.

Translation

• The second stage of protein synthesis

• Takes place at ribosomes in the cytoplasm

• Amino acids are joined together by the ribosome to create a polypeptide chain (primary protein structure)

What is translation?Once a molecule of mRNA has been transcribed, it moves out of the nucleus via a nuclear pore.

In the cytoplasm, the mRNA combines with a ribosome – the cellular structure on which the polypeptide chain will be built in a process called translation.

How are the correct amino acids transported to the ribosome, and how are they linked together in the correct order?

mRNA strand

ribosome

What is tRNA?

nucleotides

amino acidattachment site

anticodon

In the cytoplasm, amino acids become attached to transfer RNA (tRNA) molecules. Each tRNA is specific for one amino acid.

Each tRNA molecule has a sequence of three bases called an anticodon. These are complementary to codons on the mRNA molecule.

3’ end

5’ end

hydrogen bond

What is the anticodon for

the codon A U G?

U A CRemember the mRNA is the code for the amino acid attached to the tRNA

What happens during translation?tRNA molecules attach to the ribosome, and their anticodons pair up with the appropriate codons on the mRNA.

The amino acids transported by the tRNA link together, and the tRNA molecules then return to the cytoplasm.

The ribosome moves along the mRNA, and amino acids continue to join together until all the codons have been translated and the polypeptide is complete.

feature mRNA tRNA

strands

shape

Location of action

Role

Complete the table

Translation Animation• You can see from the animation that the ribosome

is essential to the process, together with the tRNAs

• Following translation the primary structure (polypeptide chain) is created.

• It is entirely dependent on the mRNA sequence• The primary structure determines the tertiary

structure of the protein.• The tertiary structure is crucial to the functioning

of the protein.

Stages of protein synthesis

From DNA to amino acids

Exam Practice• The figure below is a diagram that shows the stage in protein

synthesis when amino acids are joined in the correct sequence to make the primary structure of the protein.

• Name J to M.• The group of bases at J• K • L• The group of bases at M

[4]

KJ

L

M

am ino acid

J anticodon; R anticodonsK transfer RNA / tRNA;L ribosome / rRNA;M codon; R codons

Role of cAMP• Some proteins produced by protein synthesis

aren’t active and need to be activated before they can work.

• Just like protein synthesis, this activation is controlled by chemicals eg hormones and sugars

• Link from AS: Some molecules activate cellular processes by binding to the cell membrane and this triggers the release of a second messenger called cAMP (cyclic AMP) which then alters the 3D structure of the protein.

• This activates the protein• P107 purple book – purple box.

Learning outcome: State that cAMP activates proteins by altering their 3D structure.

Revisit Learning Outcomes

• describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes

• State that cAMP activates proteins by altering their 3D structure.

Plenary

• Using the information in the diagram to help you, explain how amino acids become arranged into the correct sequence in the primary structure of the protein.

KJ

L

M

am ino acid

Answers

• 1 DNA triplet / codon / M / mRNA triplet, codes for specific amino acid;

• 2 order of, triplets / bases, determines the order of amino acids;

• 3 tRNA / K, has, corresponding / complementary, triplet / anticodon;

• 4 (tRNA / K) attached to specific amino acid;• 5 activation of amino acid;• 6 2 (tRNA) binding sites on the ribosome;• 7 codon and anticodon bind; A match• 8 A to U and C to G;• 9 adjacent amino acids join;• 10 peptide bond; 4 max•

Homework

• Protein synthesis summary sheet (not q7)• p100 green boxes GB• P107 questions PB