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
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