1. Cell protein production
Biology ATAR & General
Human Biology ATAR & General

2. Keywords DNA Ribosomes Protein synthesis tRNA mRNA Transcription
RNA polymerase
Template strand
Coding strand
Codon
Intron
Exon
Ribosomes
tRNA
Anticodon
Translation
Start codon methionine
Protein structure
Endoplasmic reticulum (ER)
Golgi bodies

3. What does DNA code for?
DNA carries the instructions for making proteins
These instructions are organised into segments called genes.
Genes are divided into 2 categories:
Coding genes (exons)
Non-coding or regulating genes (introns)

4. Introns & exons Introns
Introns can be thought of as the chef in the kitchen. The chef decides when the cake should be made (eg. for a birthday), what kitchen appliances are to be used, how the ingredients are to mixed, what temperature the oven needs to be and how long the cake should be baked for.
Exons
Exons can be thought of as a recipe, with a list of ingredients and instructions. The ingredients being the amino acid codons, and the instructions being the sequence of assembly.

5. Review: functions of proteins
Proteins have many different functions:
Structure: the protein keratin gives strength to hair, nails etc.
Transport across membranes: some proteins form channels in cell membranes to aid the transport of molecules
Communication: many hormones are proteins.
Cell metabolism: enzymes are proteins . Enzymes help speed up the chemical reactions in a cell.
Recognition: proteins in the cell membrane are unique to a particular person
Movement: protein molecules are able to change shape and this is the basis for the movement of structures within the cell.

6. Proteins Proteins are made up of amino acids.
There are 20 different types of amino acids in the body
Most proteins are very large molecules consisting of hundreds to thousands of amino acid chains.
Coding genes (exons) specify the number and type of amino acids and the order in which they are to be assembled.

7. Protein synthesis Transcription Occurs in the nucleus
Enzyme involved: RNA polymerase
Product: mRNA
Protein synthesis occurs in 2 parts
Transcription
Translation
Translation
Occurs at the ribosome
Molecules involved: mRNA & tRNA
Product: protein

8. Transcription, translation & RNA
The DNA molecule is too large to leave the nucleus
Another molecule called ribonucleic acid or RNA is made
RNA carries the information for only one gene at a time
RNA transcribes and translates this information to make one protein
This happens at the ribosome in the cytoplasm
RNA consists of a
Ribose (a sugar)
Phosphate
Nucleotide base
RNA is slightly different to DNA.
Instead of thymine it has uracil

9. DNA vs. RNA
Thymine
(+C)
Uracil
(-C)
deoxyribose
ribose

10. Double strand
Single strand

11. Transcription, translation & RNA
There are 2 types of RNA
Messenger RNA (mRNA)
Transport RNA (tRNA)
mRNA takes the code from the DNA, across the nuclear membrane, to the ribosome in the cytoplasm
tRNA helps to build the protein by bringing the amino acids to the mRNA at the ribosome

12. Transcription Transcription is the formation of the mRNA strand
It occurs in the nucleus
The genetic instructions are copied from the DNA to the mRNA molecule
The process is very similar to DNA replication

13. Transcription
RNA polymerase is the enzyme that ‘unzips’ the double stranded DNA
It then transcribes (copies) the bases from one strand of DNA to make a complementary strand of mRNA
At the end of the gene there is a sequence of bases that tells the RNA polymerase to stop copying and the mRNA molecule is released

14. Transcription

15. Transcription
Only one of the strands of DNA is copied during transcription
This strand is called the template strand
The other strand is called the coding strand
Because the bases always form complementary pairs, the order of bases in the mRNA molecule will be the same as in the coding strand, but opposite to the template strand

16. Transcription Remember, DNA contains introns and exons
The mRNA that has been copied contains both introns and exons
Introns must be removed before the mRNA can be used to assemble amino acids into a protein

17. Introns and exons Exons DNA mRNA Intron Intron
NIH - National Human Genome Research Institute

18. Translation
Every mRNA molecule has a starting codon and a stopping codon
This ensures that protein synthesis starts at the correct end of the mRNA molecule
Translation is the process of synthesising a protein from the information contained within the mRNA
It occurs at the ribosome
It involves both mRNA and tRNA

19. Translation
The ribosome then moves along the mRNA and pulls it through like a ribbon, reading the bases as it goes

20. Translation, codons & anticodons
Every 3 base pairs form a codon
Each unique codon is associated with one type of amino acid
There are 20 types of amino acids in the body
tRNA molecules carry the complementary codon
These are called anti-codons
There are 20 types of tRNA molecules, each with its unique anti-codon on one end and carrying the corresponding amino acid on the other end

21. Translation
The tRNA molecules bring the individual amino acids to the mRNA/ribosome complex to be joined together to form the protein
The anti-codon on a tRNA molecule binds to the complementary codon on the mRNA molecule

23. Translation
The amino acids carried by the tRNA are joined together so the protein is assembled in the right order
Each bond formed between the amino acid requires 1 ATP
Once the tRNA has delivered its amino acid it detaches from the ribosome

24. Translation
NIH - National Human Genome Research Institute

25. Protein structure
After a protein has been synthesized, it must then be organised into a particular shape
Protein shape is very important for the correct functioning of the protein
Proteins have 3 or 4 levels of complexity in their structure

26. Protein structure
Primary structure: is the sequence of amino acids in the chain that makes up the protein
Secondary structure: this is either a coiled or folded shape that is brought by bonds between different parts of the amino acid chain
Tertiary structure: this is formed by further bending and folding of the protein into globular or fibrous shapes
Quaternary structure: when 2 or more chains of amino acids interact

27. Packaging of proteins
If proteins are to be used outside the cell, they must be packaged for secretion
After proteins are made at the ribosome, they travel through the ER into the golgi bodies where they are modified and packaged via exocytosis

28. Lipid and carbohydrate synthesis
DNA only contains code for the manufacture of proteins
However, it contains code for the production of enzymes (which are proteins) and therefore DNA indirectly controls the synthesis of lipids and carbohydrates

29. PROTEIN SYNTHESIS – TRANSLATION & TRANSCRIPTION
Class resources
Bozeman Science
Transcription and Translation: 12 mins
Student resources