(3) Gene Expression Gene Expression (A) What is Gene Expression? (E) Splicing and post-translational modification (B) Structure and Functions of RNA (D) Translation (C) Transcription

Gene Expression (C) State where transcription occurs Name the enzyme involved in transcription State the role of this enzyme Describe the stages of transcription State what introns and exons are State what RNA splicing is Explain the difference between the primary and mature RNA strands

Re-cap on the cell ultrastructure Nat 5s - you should know these!

Animal Cell Ultra structure Plasma membrane

Animal Cell Ultra structure Mitochondrion Produces ATP by aerobic respiration

Animal Cell Ultra structure Cytoplasm

Animal Cell Ultra structure Nuclear membrane

Animal Cell Ultra structure Nuclear Pore

Animal Cell Ultra structure Nucleolus Synthesis of RNA and ribosomes

Animal Cell Ultra structure Rough Endoplasmic Reticulum Synthesis and transport of proteins for export

Animal Cell Ultra structure Ribosomes Site of protein synthesis

Animal Cell Ultra structure Golgi Body Packages complex molecules for secretion

Animal Cell Ultra structure Golgi Vesicle Encloses and transports molecules

Animal Cell Ultra structure Lysosome Contains digestive enzymes

Animal Cell Ultra structure Smooth Endoplasmic Reticulum Synthesis and transport of lipids

Animal Cell Ultra structure Small vacuole

Animal Cell Ultra structure Centriole Involved in the formation of spindle fibres

Animal Cell Ultra structure Fluid filled pinocytic vesicle

Re-cap – cell ultrastructure Cell membrane Fluid filled vesicle Cytoplasm Mitochondria Nuclear membrane Centrioles Nuclear pore Small vacuole Nucleus Nucleolus Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum ribosomes Golgi Body Lysosome Golgi Vesicle

Pathway to making a protein DNA (containing all the genetic material / coding) “The middle man” Protein messengerRNA

Pathway to making a protein DNA RNA Protein a mRNA molecule is made (transcribed) from a portion of DNA and then carried to the cytoplasm transcription translation occurs when the sequence of bases of mRNA DIRECTS the sequence of amino acids in a protein RIBOSOME – site of protein synthesis

Where does transcription occur? Where do you find the DNA? Where is protein made? DNA never leaves the nucleus just incase it becomes damaged! Therefore the DNA is transcribed (copied) into mRNA inside the nucleus Education Scotland - TRANSCRIPTION ANIMATION

Notice Uracil Cytoplasm Nucleus PORE IN THE NUCLEAR MEMBRANE G A T C G A T C PORE IN THE NUCLEAR MEMBRANE SECTION OF DNA UNWOUND C A G U SECTION OF DNA UNWOUND AND UNZIPPED mRNA MOLECULE FORMING C A G U mRNA transcript PASSING THROUGH THE POREIN NUCLEUS Notice Uracil

transcription Step 1: Transcription can only take place if the enzyme RNA polymerase is present RNA polymerase is built at the promoter region of DNA (region where transcription is initiated)

transcription Step 2: RNA polymerase moves along the DNA, unwinding and unzipping the double helix by breaking the weak hydrogen bonds between the complementary base pairs

transcription Step 3: RNA polymerase joins RNA nucleotides together and synthesises a primary mRNA transcript by complementary base pairing Only 1 DNA strand is used as template for transcription. The DNA strand is read from the 3’ to 5’ direction Free RNA nucleotides join on to the 3’ end of the growing mRNA strand. Hydrogen bonds form between complementary base pairs.

transcription Step 4: mRNA continues to grow until a terminator sequence on the DNA strand is reached. The mRNA and RNA polymerase become separated from the DNA strand. This mRNA strand is called the primary transcript. The DNA strands wind back up to form the double helix.

transcription Step 5: Splicing of the mRNA strand takes place. Genes have introns (non-coding regions of genes) and exons (coding regions of genes). The introns are removed in RNA splicing. The exons are joined together to form mature transcript. This process is called RNA splicing.

transcription Step 6: The mature mRNA transcript leaves the nucleus through the nuclear pores and enters the cytoplasm

Transcription of DNA into primary and mature RNA transcripts in the nucleus ribosome

Codons A triplet of bases on the mRNA template codes for 1 amino acid. This triplet of bases is called a CODON. A U G C mRNA start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1

Codons DNA strand: A-T-C – T-G-C – A-G-T mRNA strand: A triplet of bases on the mRNA strand codes for 1 amino acid. This triplet of bases is called a CODON. U-A-G A-C-G U-C-A codon 2 codon 3 codon 1

Notice Uracil Codon 2 Codon 1 Cytoplasm Nucleus G A T C G A T C PORE IN THE NUCLEAR MEMBRANE SECTION OF DNA UNWOUND C A G U SECTION OF DNA UNWOUND AND UNZIPPED mRNA MOLECULE FORMING C A G U mRNA transcript PASSING THROUGH THE POREIN NUCLEUS Notice Uracil RNA Splicing Codon 2 Codon 1 U C A G Splicing RNA attaches to ribosome

TASK Collect a diagram and tick it into your jotter Describe what is happening at each step (1-8)

Questions A gene has coding sections – what are these called? A gene also has non-coding sections – what are these called? Which of these is removed from the primary transcript of mRNA? By what process? During transcription, all of the genetic information in a gene is initially copied into an RNA molecule - What is this called? What enzyme is responsible for transcription? The initial RNA molecule is ‘spliced’ – Explain what this means and why the cell does this. What name is given to the final mRNA which moves out of the nucleus into the cytoplasm? Draw a diagram of the mRNA strand that would be transcribed from section X of the DNA molecule below: Section X A T C G G G C C A A T T A G C C C G G T T A

Gene Expression (C) State where transcription occurs Name the enzyme involved in transcription State the role of this enzyme Describe the stages of transcription State what introns and exons are State what RNA splicing is Explain the difference between the primary and mature RNA strands