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

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

What makes species different?

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.

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.

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

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

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

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

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

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

DNA to Protein

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

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

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.

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

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

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.

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.

Modification

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