A closer look at protein synthesis for Year 10 students at Saint Ignatius College Geelong

1. GENETICS.
03. Protein synthesis.
Ian Anderson
Saint Ignatius College Geelong

2. PROTEINS.
 Proteins are polymers built up of amino acid
monomers.
 Proteins play a key role in living organisms.
 They have specific roles.
 Structural e.g. collagen, keratin.
 Regulatory e.g. insulin, glucagon, adrenalin.
 Enzymes e.g. amylase, pepsin.
 Transport e.g. haemoglobin.
 Each cell contains several hundred to several
thousand proteins.
 Human proteome estimated >100 000.

3. PROTEINS.
Everything a cell is or does depends on the proteins
it contains.
Source:
http://www.etap.org/demo/grade7_science/instruction1tutor.html

4. PROTEIN SYNTHESIS.
 DNA carries the sets of instructions in the
chromosomes for every part of an organism,
including the production of proteins.
 Proteins however are manufactured on ribosomes
located in the cell cytoplasm.
 So a method is needed to transfer the information
needed to build a protein from the DNA to the
ribosomes.

5. PROTEIN SYNTHESIS.
 DNA stays in the nucleus and another molecule,
acting as a messenger, carries the instructions
from the DNA to the ribosomes.
 Proteins can now be manufactured by the
ribosomes.
 This two stage process = protein synthesis.

6. PROTEIN SYNTHESIS.
Two stages of protein synthesis
 Transcription
 Translation

7. TRANSCRIPTION.
Messenger RNA (mRNA) is made.
 A single-stranded ‘copy’ of the DNA segment that
codes for the required protein.
 Steps:
1. Relevant segment of DNA unwinds forming two
single strands.
2. Free floating nucleotides in nucleus bind to one
strand following the base pairing rule.
 adenine  uracil (not thymine)
 cytosine  guanine
3. Complementary copy of DNA, called messenger
RNA (mRNA) is formed.

8. DNA V RNA.
DNA RNA
Contains the sugar deoxyribose Contains the sugar ribose
Contains the bases
• Adenine (A)
• Cytosine (C)
• Guanine (G)
• Thymine (T)
Contains the bases
• Adenine (A)
• Cytosine (C)
• Guanine (G)
• Uracil (U)
A double-stranded molecule
• Has a double helix shape
A single-stranded molecule
Found in the cell nucleus
[also found in mitochondria and
chloroplasts]
Three types
• mRNA
• tRNA
• rRNA

9. TRANSCRIPTION.
Source:
http://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/

10. TRANSCRIPTION.
Source:
http://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/
 The‘message’ from the DNA can now translated.

11. TRANSLATION.
The synthesis of a protein from mRNA.
 Steps:
1. mRNA leaves the nucleus and travels into
cytoplasm and attaches to a ribosome.
 Each sequence of three bases on the mRNA is called a codon
(triplet code) and codes for a particular amino acid.
2. Transfer RNA (tRNA) molecule with a
complementary base triplet (called an anticodon)
carries specified amino acid to ribosome.
3. Amino acids are linked with peptide bonds to form
a polypeptide.

12. DECIPHERING THE GENETIC CODE.
 During translation the mRNA is read in sets of
three nucleotides (codons).
 There are more different combinations of codons than
what there are naturally occurring amino acids.
 All possible combinations of the four bases (A, C, G, U)
result in 64 (43) three letter codons.
 20 naturally occurring amino acids.
 Meaning that there are more than one codon for most
amino acids i.e.
 e.g. CUU, CUC, CUA & CUG all code for the amino acid
Leucine.

13. TRANSLATION.
Source:
http://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/

17. PROTEIN SYNTHESIS.
Head on over to
http://learn.genetics.utah.edu/content/molecules/transcribe/
And make your own protein!

18. http://SICkScience10.wikispaces.com/