Leaving Cert BiologyGenetics – section 2.5

Genetics 2.52.5.4( RNA), 2.5.5, 2.5.15

Leaving Cert BiologyGenetics – section 2.5

2.5.4 RNA Structure

• It is made up of nucleotide units

• Each nucleotide unit has a backbone one of four nucleotide bases:

Adenine A,

Guanine G,

Cytosine C,

and Uracil U (instead of thymine!)

U

• RNA (ribonucleic acid) is another nucleic acid.

Leaving Cert BiologyGenetics – section 2.5

RNA Structure

Unlike DNA,

RNA is single stranded!

Leaving Cert BiologyGenetics – section 2.5

2.5.5 Protein synthesis

• Every protein has a particular sequence of amino acids that it is made up of.

3-D image of Melanin

1. Our DNA contains the instructions (in the form of a code) to make proteins

Leaving Cert BiologyGenetics – section 2.5

Protein synthesis2.The code contained in our DNA is transcribed (copied)

to make messenger RNA (mRNA).

Leaving Cert BiologyGenetics – section 2.5

3. The mRNA carries the code into the ribosome

Protein synthesis

The mRNA

The protein chain

Leaving Cert BiologyGenetics – section 2.5

The function of mRNA in protein synthesis is to carry a copy of the DNA instructions (codes) from the nucleus to the ribosomes.

Leaving Cert BiologyGenetics – section 2.5

Protein synthesis4. In the ribosome the code is translated and the amino acids are assembled into the correct sequence to make the protein.

Leaving Cert BiologyGenetics – section 2.5

Protein synthesis5. The protein folds into its functional shape.

Leaving Cert BiologyGenetics – section 2.5

Protein synthesis – higher level

• 1. Enzymes unwind the double helix

Leaving Cert BiologyGenetics – section 2.5

• RNA nucleotide bases bond with one strand of exposed DNA. • The enzyme RNA polymerase assembles these bases to

form mRNA.

2. Transcription

•mRNA has a series of bases that are complementary to those in DNA !

Leaving Cert BiologyGenetics – section 2.5

The function of mRNA in protein synthesis is to carry a copy of the DNA instructions (codes) from the nucleus to the ribosomes.

Leaving Cert BiologyGenetics – section 2.5

Leaving Cert BiologyGenetics – section 2.5

• mRNA moves into the cytoplasm

• Each three base sequence of mRNA carries a genetic code (codon) that specifies either:

a starting codon,

a particular amino acid

or a stop codon.

3. mRNA sequence

Leaving Cert BiologyGenetics – section 2.5

• Ribosome subunits (rRNAs) attach to the mRNA.• These subunits form the ribosome, the site of protein

synthesis.

4. The ribosome

Leaving Cert BiologyGenetics – section 2.5

• Free floating tRNAs with their attached amino acids, within the cytoplasm are attracted to the complementary mRNA already attached to the ribosome.

• This ensures the amino acids are aligned in a sequence determined by the codons of the mRNA

5. tRNA

Leaving Cert BiologyGenetics – section 2.5

• Aligned amino acids bond to form links of the new protein molecule

6. Protein synthesis

Leaving Cert BiologyGenetics – section 2.5

• tRNAs continue to move to the ribosome, until a stop codon on the mRNA code sequence tells the ribosome that the process is complete and the protein is synthesised.

7. End of Translation

Leaving Cert BiologyGenetics – section 2.5

8. Protein folding5. The protein folds into its functional shape.

Can you..

• Tell what RNA stands for

• Explain how mRNA is made

• Give the function of mRNA

• Tell the location of transcription

• Describe what happens to mRNA after it leaves the nucleus

• Explain how the code of mRNA is translated

Leaving Cert BiologyGenetics – section 2.5