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Genetics lecture 5- Transcription

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winniesmith1's version from 2017-05-14 13:15

Section 1

Question Answer
What is the central dogma of biology (eg. how is DNA turned to proteins)DNA transcribed to RNA and translated to protein
What is a geneA functional unit of DNA.
Describe steps from transcription to functionTranscribed sequence, with exons and introns. Transcription and splicing causes introns to be removed in mRNA. Translation makes the sequence into a protein which is then folded for its function.
Where does translation occurIn the cytoplasm
How many AA are used by living organisms20
What is the genetic code Universal code which must be able to specify all 20 AAs. Gives triplet code.
What is the triplet code4 nucleotides, can be put together in 64 different ways to code for 20 amino acids (21 with STOP codon). It is redundant (degeneracy). One amino acid will have multiple codons (said to be degenerate for this reason). Each codon specifies the AA to be placed in corresponding position along polypeptide. Move from 5' to 3' direction.
What is known as the start codonmethionine (AUG)
Which codes specify termination to translation3- UAG, UAA, UGA. STOP codons
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Section 2

Question Answer
What is translationconverting from one language to another , in this case mRNA to Amino acids.
What else does the cytoplasm require for translation to occuradditional types of RNA; rRNA, tRNA and snRNA.
What does mRNA doattaches small ribosomal subunit. Carries info specifying amino acid sequence of proteins from DNA to ribosomes.
what does tRNA docarrys methionine to attach to the intiation codon (AUG)--> Large ribosomal subunit attaches to make complete ribosome. Serves as translator molecule in protein synthesis; translates mRNA codons into amino acids.
what does rRNA doplays catalytic (ribozyme) roles and structural roles in ribosomes.
what is the function of a primary transcript (RNA)is a precursor to mRNA, rRNA or tRNA, before being processed; some intron RNA acts as a ribozyme, catalyzing its own splicing.
what is the function of small nuclear RNA (snRNA)Plays structural and catalytic roles in spliceosomes, the complexes of protein and RNA that splice pre-mRNA.
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Section 3

Question Answer
TRANSLATION. What are the 4 steps in which information in mRNA is translated into the primary sequence of a protein1) activation. 2) initiation. 3) elongation. 4) termination.
What happens in the activation stage-Each amino acid activated by reacting with ATP. -tRNA synthetase enzyme attaches activated amino acid to own particular tRNA
What happens in the initiation stage -mRNA attaches to smaller body of ribosome. -Initiator tRNA attaches to start codon. -Larger body of ribosome combines with smaller body.
What happens in the elongation stage-Anticodon of next tRNA binds to mRNA codon at A site of ribosome; Each tRNA specific for one amino acid only, but some amino acids coded for by up to 6 codons; Order of bases in mRNA codons determine which tRNA anticodons will align and therefore determines order of amino acids in protein. -Amino acid at A site linked to previous amino acid. -Ribosome moves along one codon and next tRNA binds at A site
What happens in the termination stage -Final codon on mRNA contains termination signal (STOP Codon ā€“ UAA, UAG, UGA). -Releasing factors cleave polypeptide chain from tRNA that carried final amino acid. -mRNA released from ribosome and broken down into nucleotides.
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Section 4

Question Answer
what are ribosomes made up of 2/3 rRNA and1/3 proteins. Millions of daltons. fast and efficient (2aa)
what is a daltona unit used in expressing the molecular weight of proteins, equivalent to atomic mass unit.
what are ribosomes Powerhouse of cell. Ribosomes are complex macromolecular assemblies of protein and RNA (ribosomal RNA and rRNA)
what is a ribosome the equivalent of a ribozyme.
describe the main constituent of ribosomesrRNA. highly packed, precise 3D shape, proteins 'fill' the gaps.
In ribosomes the rate of initiation equals whatRate of protein synthesis
Describe ribosomes of prokaryotic cellsThey consist of three kinds of rRNA and about 50 types of proteins. Large peptide bond formation.
Describe ribosomes of eukaryotic cellsMore complex. Consisting of five kinds of rRNA and about 80 kinds of proteins. Small tRNA-mRNA.
What are ribosomes composed ofA large and small subunit, which perform different tasks
What is the small subunit responsible forbinding the mRNA, interacting with the anti-codon end of the tRNA, to ensure the correct codon- anticodon interaction between mRNA in tRNA
What is the large subunit responsible forFor peptide bond formation in the growing peptide chain, interacting with the aminoacyl-bound end of the tRNA
Size of large subunit50S in bacteria and 60S in eukaryotes.
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Section 5

Question Answer
Describe tRNA in translation, activation stage(80n) high level of self complementarity ā€“ cloverleaf structure. Anticodon. 3' amino acid site. Amino acytl-tRNA synthetases (to join amino acids).
Describe translation; initiation.Small ribosomal subunit + translation initiation factors (TIGs) = P site. Small subunit binds to 5' mRNA end (Cap). Moves 5' to 3' to find AUG. AUG pre-bound to initiator mRNA (Met) P site. AUG location= dissociation of TIFs and gain large ribosomal subunit.
Describe elongationSecond amino acid joins initiation complex. First peptide bond forms as new amino acid arrives. Amino acid chain extends.
Describe translation; elongation. part 1The tRNA attached to the growing peptide chain is on the P-site of the small ribosomal subunit. The incoming aminoacyl-tRNA (aa-tRNA) binds to the A-site of the small ribosomal subunit. The peptidyl-tRNA on the P-site donates the peptide chain to the aa-tRNA on the A-site through peptide bond formation.
Describe translation; elongation part 2Following this transfer, the A-site tRNA moves with the peptide to the P-site, while the deacylated tRNA on the P-site moves to the E-site (exit site), before detaching from the ribosome. This leaves the A-site free for the next aa-tRNA to bind. The elongation procedure is carried out by three important proteins known collectively as elongation factors.
Describe translation; elongation part 3Amino acid chain continues to grow via mRNA:tRNA bp complementarity. Final codon on mRNA contains termination signal (STOP Codon)
Describe translation; terminationFinal codon on mRNA contains termination signal (STOP Codon). A-site = stop codon enables releasing factors to bind. Releasing factors cleave polypeptide chain from tRNA that carried final amino acid (free CO2H - Cā€™ terminal of polypeptide). mRNA released from ribosome and broken down into nucleotides. Free polypeptide ā€“ spontaneous folding.
What is the finished product of translationCytosolic protein. Spontaneous folding. Organise folding. Post-translation modification.
What processes occur in post-translational modificationGlycosylation, Phosphorylation, Ubiquitination, Acylation, Deamination, Methylation.
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Section 6

Question Answer
What is a mutationthe changing of the structure of a gene, resulting in a variant form which may be transmitted to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.
Describe mutationsHaritable change in DNA. Basis for genetic variability, Harmful, neutral, or beneficial! Mutation is a normal process!
What is the mutation rate(Human genome- diploid. 6 billion base pairs replicate before cell divides) Mutation rate - 6 - 60 bp/generation
Where do heritable mutations occurGerm cells
How many ways can a codon be mutated9 possible ways
Describe large-scale chromosome-wide mutationsTranslocations, inversions, deletions, insertions.
Describe small-scale mutationsPoint mutations, Indels, frameshift
Describe point mutationsChanges in one or a few nucleotides. Can be; substitution, insertion, deletion.
What is a transitionPurines to purines or pyrimidines to pyrimidines.
What is a trasversionPurine to pyrimidines or vise versa.
What is a synonymous substitutionA silent substitution. For example; same amino acid coded for, despite mutation.
What is a non-synonymous substitutionA replacement substitution. Mutation causes different amino acids to be coded for.
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Section 7

Question Answer
What are frameshift mutationsshifts the reading frame of the genetic message so that the protein may not be able to perform its function. Can be caused by insertion or deletion.
What happens in a chromosome mutationChanges in the number and structure of the entire chromosome --> changes order of genes. Can be caused by; deletion, duplication, inversion, translocation.
Significance of mutations; most are neutral such asEye colour and birthmarks
Significance of mutations; some are harmful such asSickle-cell anaemia and Down syndrome.
Significance of mutations; some beneficial such asSickle cell anaemia to malaria and and immunity to HIV.
What are two ways in which DNA can become mutatedCan be inherited (parent to child) or acquired (environmental damage or mistakes when DNA is copied)
What is DNA continually assaulted byDamaging agents (oxygen free radicals, ultraviolet light, toxic chemicals)
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