Ib Biology HL : Protein synthesis - D.1.2

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27 Terms

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transcription

3’ to 5’ is the template strand: the one used by the mRNA.

helicase opens the DNA. RNA polymerase catalyses the production of mRNA. The mRNA is essentially the same as the coding strand

<p></p><p>3’ to 5’ is the template strand: the one used by the mRNA. </p><p>helicase opens the DNA. RNA polymerase catalyses the production of mRNA. The mRNA is essentially the same as the coding strand</p>
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What directions do polymerases read genetic material and how do they produce new ones ?

Read from 3’ to 5’

Produce new strand 5’ to 3’

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What order is mRNA read in ribosomes ?

5’ to 3’

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percentage of expressed genes

25% - in whole body !

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genes expression variation:

  • genes related to essential metabolic reactions: respiration. always

  • at later stage: stem→ specialised

  • matured cells → memory B cells

  • when signalled to→ insulin production

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Point mutation

Mutation in which one nucleotide is changed. Usually happens in dna replication but can also happen in transcription

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Types of point mutation

  • insertion mutation

  • Deletion mutation

Both of these cause frameshift mutation, meaning that all the following codons are affected by the mutation

  • substitution mutation: due to code degeneracy, it sometimes is a silent mutation

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Élongation of a polypeptide

  1. tRNA comes and bonds to A site

  2. The large subunit of the ribosome catalyses a reaction between the amino acid held by the tRNA in the A site and the one in the P site ( requires energy )

  3. tRNA in P site moves to E site and exits ribosome, and one in A site moves to P site ( requires energy ) which leaves site A available for next tRNA

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proteome

All cells used by human body

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Proteasome

protease complex which degrades and recycles unwanted proteins: hydrolyses peptide bonds between amino acids

collaborates with ubiquitin, which binds to the unwanted proteins

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Stages of translation

  • initiation: mRNA attaches to small subunit of ribosome

  • Elongation: peptide bonds are for,Ed

  • TerminAtion: polypeptide released during termination

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stages of elongation

  • hydrogen bonds to A part of ribosome on tRNA

  • ATP used up to form covalent/ peptide bond between amino acids

  • amino acids moves to T

  • eventually exits

  • continues until reaches stop codon

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The promoter DNA

Non coding region in DNA just before a gene, where proteins known as positive transcription factors can bind, which will allow the RNA polymerase to bind to the dna

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Non coding sequences in DNA roles

  • regulators of gene expression : promoters

  • Introns: parts of dna that are copied in mRNA but removed in post transcriptional modification

  • Telomeres: parts at end of chromosomes made of repetitions which protects coding DNA; with every cell division 0, end of the telomeres are lost

  • Genes for tRNA and rRNA ; ?

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Directionality of transcription

Direction of RNA polymerase when on DNA (5’ to 3’);

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Post transcriptional modification of mRNA

  • addition of 5’ cap ( so ribosome can work )

  • a poly-A-tail ( which protects a molecule from degradation )

  • Splicing : excising introns ( splisosomes ) : and ligating exons to form mature mRNA

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Introns and exons

Introns In eukaryotic genomes, don’t contain coding information. Exons do; they code for polypeptides

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Alternative splicing

A gene can be modified by combing different exons and removing others; this can results in a different range of proteins which function differently. Like this, from a single gene multiple proteins can be made

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polysome

several ribosomes may move along the mRNA at the same time. This structure ( mRNA, ribosomes and protein chains ) is called a polysome

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Alternative splicing example

Troponin P, a protein involved in cardiac contraction, is sliced one particular way in foetuses which gives it a greater sensitivity to Ça+2 and acidosis. A few weeks after the birth of the baby, the troponin T gene gets spliced differently and these features are lost

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what direction is mRNA synthesised

5’ to 3’ on the template stand which is 3’ to 5’

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transcription bubble

  • RNA polymerase

  • mRNA strand

  • template DNA

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non coding regions of dna ( list them )

  • promoter

  • terminator

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promoter

  • marks the beginning of the protein sequence

  • in charge of deciding weather or not the gene gets transcribes

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terminator

  • when they are transcribed, the DNA polymerase detaches and therefore stops the transcription process

  • allows it to not make a huge, useless protein

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describe structure visible (3)

  • alpha helixes and beta pleated sheets cause secondary structure

  • the 3D structure of chain A and chain B shows the secondary structure

  • the combination of structure A and structure B leading to a globular structure shows quartermary structure

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