Leaving Cert Biology
Genetics – section 2.5
Genetics 2.5
2.5.4( RNA), 2.5.5, 2.5.15
Leaving Cert Biology
Genetics – section 2.5
2.5.4 RNA Structure
• RNA (ribonucleic acid) is another nucleic acid.
• 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
Leaving Cert Biology
Genetics – section 2.5
RNA Structure
Unlike DNA,
RNA is single stranded!
Leaving Cert Biology
Genetics – section 2.5
2.5.5 Protein synthesis
• Every protein has a particular sequence of amino acids
that it is made up of.
1. Our DNA contains the
instructions (in the form of a
code) to make proteins
3-D image of Melanin
Leaving Cert Biology
Genetics – section 2.5
Protein synthesis
2.The code contained in our DNA is transcribed (copied)
to make messenger RNA (mRNA).
Leaving Cert Biology
Genetics – section 2.5
Protein synthesis
3. The mRNA carries the code into the ribosome
The mRNA
The protein chain
Leaving Cert Biology
Genetics – 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 Biology
Genetics – section 2.5
Protein synthesis
4. In the ribosome the code is
translated and the amino
acids are assembled into the
correct sequence to make the
protein.
Leaving Cert Biology
Genetics – section 2.5
Protein synthesis
5. The protein folds into its functional shape.
Leaving Cert Biology
Genetics – section 2.5
Protein synthesis – higher level
• 1. Enzymes unwind the double helix
Leaving Cert Biology
Genetics – section 2.5
2. Transcription
• RNA nucleotide bases bond with one strand of exposed DNA.
• The enzyme RNA polymerase assembles these bases to
form mRNA.
•mRNA has a series of bases that
are complementary to those in
DNA !
Leaving Cert Biology
Genetics – 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 Biology
Genetics – section 2.5
Leaving Cert Biology
Genetics – section 2.5
3. mRNA sequence
• 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.
Leaving Cert Biology
Genetics – section 2.5
4. The ribosome
• Ribosome subunits (rRNAs) attach to the mRNA.
• These subunits form the ribosome, the site of protein
synthesis.
Leaving Cert Biology
Genetics – section 2.5
5. tRNA
• 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
Leaving Cert Biology
Genetics – section 2.5
6. Protein synthesis
• Aligned amino acids bond to form links of the new
protein molecule
Leaving Cert Biology
Genetics – section 2.5
7. End of Translation
• 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.
Leaving Cert Biology
Genetics – section 2.5
8. Protein folding
5. The protein folds into its functional shape.
Leaving Cert Biology
Genetics – section 2.5
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