1. Gene Expression and Protein Synthesis
Higher Human Biology
Sub-topic 3

2. Learning Intentions
State the three types of RNA and give their function
Describe the structure of RNA
Describe the process of protein synthesis

3. What makes species different?

4. Genotype
- genetic make up of an organism
- determined by the sequence of the DNA bases in its genetic code.
Phenotype
physical / chemical appearance
determined by the proteins that are synthesised when the genes are expressed.

5. Function of RNA RNA is a nucleic acid with a similar structure to DNA.
The role of RNA is in producing proteins where each type of RNA has a specific function.

6. RNA Structure
RNA is a single stranded molecule made up of units called nucleotides.
Nucleotides are made of 3 parts:
RIBOSE SUGAR

7. Differences between RNA and DNA
Number of strands
Complementary base pair of adenine
Sugar present in nucleotide

8. Base Pairing There are 4 bases : Adenine pairs with URACIL
Guanine pairs with cytosine

9. Types of RNA
Messenger RNA (mRNA) – carries the genetic information from the nucleus to the ribosome for protein synthesis (DNA can’t leave the nucleus)
mRNA
RIBOSOME
NUCLEUS

10. Types of RNA
Transfer RNA (tRNA) – Carries specific amino acids to the ribosome to build into proteins

11. Ribosomal RNA (rRNA) – along with proteins it forms the ribosome
Types of RNA
Ribosomal RNA (rRNA) – along with proteins it forms the ribosome

12. DNA to Protein

13. Protein synthesis
Proteins are made by joining amino acids together in a specific sequence determined by the order of bases on DNA.

14. Protein synthesis There are 3 stages : Transcription Splicing
Translation
You need:
DNA template
Free RNA nucleotides
Enzymes (RNA polymerase
ATP

15. STAGE 1 : TRANSCRIPTION Occurs in the nucleus
STAGE 1 : TRANSCRIPTION Occurs in the nucleus. The information on DNA has to be copied onto mRNA. The enzyme RNA polymerase unwinds the DNA strand and forms the new mRNA template.

16. The Stages………… 1 – DNA unwinds
2 - RNA polymerase binds to promotor sequence on DNA
3 – weak hydrogen bonds breaking between bases, causing DNA
strands to separate
4 – free RNA nucleotides find complimentary pair on the DNA strand
(forming weak hydrogen bonds). They join at the 3’ end.
5 – strong chemical bonds are formed between the new RNA
nucleotides, opposite the DNA. This allows a new mRNA strand to
be formed

17. 6 – terminator sequence is reached on DNA and mRNA detaches from
DNA template
7 – new mRNA leaves the nucleus through pores and goes into the
cytoplasm
8 – weak hydrogen bonds form between the two original DNA
strands. DNA winds back up.
transcription animation

18. But………
Before the mRNA that leaves the nucleus it must be modified to remove non-coding regions of code.
We call the original mRNA strand the primary transcript.

19. Stage 2 - Gene Splicing The primary transcript is made up of ……
- INTRONS : non coding regions
- EXONS : coding regions
We only want the CODING REGIONS on our mRNA so we cut out the introns and splice together the exons.
The mature transcript is now ready to leave the nucleus.

20. Modification

22. Learning Intentions
State the three types of RNA and give their function
Describe the structure of RNA
Describe the process of protein synthesis