1. Human Cells Gene Expression
Higher Human Biology
Human Cells
Gene Expression

2. How do genes control protein synthesis?
In this topic you will be
Revising your knowledge on protein synthesis
Learning more details on protein synthesis
Revising your knowledge on RNA
Learning more about the structure and function of RNA
Learning more about how genes control phenotype
Learning more about what controls gene

3. N5 Revision
What can you remember from N5 about how proteins are synthesised?
Draw a diagram to detail all you know about protein synthesis and RNA

4. How does DNA code for life?
There are approximately 3 billion base pairs in our DNA
The DNA is organised into genes
Genes contain a sequence of bases that code for specific proteins
The sequence of bases are unique
Humans have 20,000 to 25,000 essential genes
This only makes up a small part (1 - 2%) of all the DNA
Scientists are still working on what the other DNA does

5. What is all the DNA doing?
When RNA is produced not all is coding for protein production.
The parts for the RNA coding to produce proteins are called Exons.
The parts of the RNA are not coding for proteins are called Introns.
When RNA is produced sections of the code must be removed (spliced out) as they are not needed.

6. Cell DNA All somatic cells contain a full complement of chromosomes
These chromosomes are the cells genotype
These chromosomes determine the phenotype of the cell
This is because the DNA is a sequence of bases that code to make protein if they are expressed by a cell
Only a fraction of genes are expressed in cells

7. Gene expression
Gene expression is affected by many factors acting both inside and outside the cell
These are intra and extra cellular environmental factors
They include chemicals such as hormones and enzymes as well as time and space
Gene expression includes 2 processes
Transcription
Translation

8. Another type of nucleic acid
DNA is a type of nucleic acid and forms the genetic code
Gene expression involves another type of nucleic acid RNA (ribonucleic acid)
RNA is different to DNA
Feature
DNA
RNA
Number of nucleotide strands 2 1
Base paring with adenine
thymine
uracil
Sugar present
deoxyribose
ribose

9. Types of RNA There are 3 types of RNA to consider
mRNA – the single strand copy produced from the DNA
tRNA – the single strand molecule that transfers a specific amino acid and aligns it with the mRNA
rRNA – RNA associated with the ribosomes

10. Transcription
At gene expression only a small portion of DNA will be copied to produce mRNA
The section to be copied has a promoter and a terminator segment
This ensures copying starts and finishes at the correct points
Transcription is controlled by an enzyme RNA polymerase

11. RNA polymerase
This enzyme is responsible for controlling unwinding, unzipping and the construction of the nucleotide strand of mRNA
This enzyme can only join nucleotides to the strand using the free 3C end of the next nucleotide
Complementary base pair rules apply except RNA has Uracil (U) instead of thymine (T)
This initial process produces the primary transcript of mRNA

12. Primary transcript

13. Transcription – modifying the initial mRNA
The primary transcript contains the essential sequence of code to produce a specific protein (exons)
These are interspersed with non coding regions called introns
In the nucleus the mRNA has these non-coding regions (introns) removed (cut out)
The exons are spliced together to produce the continuous code for the protein
This changed mRNA is called the mature transcript
This process is called RNA splicing

14. RNA splicing

15. Overview transcription

16. Consolidation Draw your own diagram to show this process
Answer questions on page 37 in the text book
Look at scholar

17. Translation
This is the process of converting the message on the mRNA into a protein molecule
It takes place at ribosomes in the cytoplasm
The mRNA is a series of base triplets or codons
A codon will be complimentary to a sequence of 3 bases on a tRNA molecule (anticodon) carrying a specific amino acid

18. Ribosomes
Ribosomes contain rRNA and enzymes essential for protein synthesis

19. Ribosomes
Ribosomes have 1 binding site for mRNA and 3 binding sites for tRNA (E, P, A)
mRNA binding site ensures mRNA is in correct position
A allows a tRNA molecule carrying an amino acid to position correctly
P holds the growing polypeptide chain as the peptide bond forms between adjacent amino acids
E releases the tRNA to be re-used as necessary

20. tRNA A short section of folded RNA
H bonds between nucleotides ensure only 3 nucleotides are exposed
These 3 nucleotides form the anticodon and will have a complimentary sequence to a codon
The amino acid specific to this anticodon is carried by the tRNA

21. Start and stop codons
tRNA will have start and stop codons so that the process of translation has a beginning and end
The start codon must be at position P to enable the polypeptide chain to start forming
tRNA enters at A proceeds through P and onto E
Amino acids are joined together with peptide bonds
Proteins are called polypeptides
Further folding and coiling would then happen to the polypeptide chain

23. One gene – many proteins

24. One gene – many proteins
Because the exons can be spliced and joined in a number of combinations then one gene could code for more than one protein
Exons and introns on the mRNA can be treated differently to give variety n the code sequence
Proteins can under transformations after forming by the addition of other molecules such as carbohydrates or phosphate groups
e.g. mucus is a glycoprotein, haemoglobin has iron added
Polypeptide strands can be cleaved to become active such as some digestive enzymes

25. mRNA codon table

26. Consolidation Chapters 1-3 homework booklet
Draw out the process of translation and label it
Text book questions on page 43
Multiple choice book chapter 3 questions
Scholar
Review PPT from school website and make own notes
Chapters 1-3 homework booklet