A2 OCR Biology - Protein Synthesis

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  • Created by: Jess
  • Created on: 18-04-14 12:18
What is DNA known as?
A polynucleotide
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What are the 3 things that make up DNA?
Pentose sugar (deoxyribose), phosphate group and nitrogenous base
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What do the bases A, T, C and G stand for?
Adenine, thymine, cytosine and guanine
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What do DNA nucleotides form when they join together?
A polynucleotide strand
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What do genes code for?
Proteins
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What is a codon?
A sequence of 3 bases in a gene that codes for an amino acid
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Why does DNA have to be copied onto mRNA before it leaves the nucleus?
Because the DNA itself is too large to move out of the nucleus
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What is the role of mRNA?
To carry the genetic code from the DNA in the nucleus to the cytoplasm where it's used to make a protein during translation
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Where is tRNA found?
In the cytoplasm
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What is the role of tRNA?
To carry the amino acids that are used to make proteins to the ribosomes during translation
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Summarize transcription
Copying the DNA strand onto a piece of mRNA
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Describe transcription
RNA polymerase attaches to DNA double-helix, breaks H-bonds/uncoils, 1 strand used as template, RNA p. lines up free RNA nucleotides, complementary base pairs, joined together, mRNA assembled, H-bonds, uncoiled strands reform, stop codon, detaches
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How does the mRNA leave the nucleus and what does it do next?
Through a nuclear pore - then attaches to a ribosome in the cytoplasm
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What is the enzyme that works during transcription?
RNA polymerase
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Summarize translation
Amino acids are joined together to make a polypeptide chain (protein) following the codon sequence carried by the mRNA
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Describe translation
mRNA attaches to ribosome, tRNA carries aminos to ribosome, tRNA accaches anticodon to 1st codon on mRNA (complementary bp), 2nd tRNA brings next amino, peptide bond joins aminos, (1st) tRNA moves away, 3rd tRNA binds to next mRNA codon, stop codon
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What is the final stage of translation?
The protein moves away from the ribosome
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How can protein synthesis be controlled?
By altering the rate of transcription of genes - increased transcription produces more mRNA which makes more protein
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What things are involved during the genetic control of protein production in prokaryotes?
Operons
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Define an operon
A section of DNA that contains structural genes, control elements and sometimes a regulatory gene
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What are the structural genes on an operon?
Z and Y, genes that code for useful proteins
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What makes up the control elements of an operon?
Promotor and operator
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What is a promotor?
A DNA sequence located before Z/Y that RNA polymerase binds to
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What is an operator?
A DNA sequence that proteins called transcription factors bind to
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What is a regulatory gene?
I - A gene that codes for a transcription factor
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What is a transcription factor?
A protein that binds to DNA and switches genes on or off by increasing or decreasing the rate of transcription
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What are the transcription factors that increase the rate of protein synthesis?
Activators
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What are the transcription factors that decrease the rate of protein synthesis?
Repressors
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What does the shape of the transcription factor determine?
Whether it can bind to DNA or not
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What substance does E. coli normally respire?
Glucose - but will use lactose if glucose isn't available
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What does the structural gene Z, on the lac operon, code for?
B-galactosidase (enzyme)
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What does the structural gene Y, on the lac operon, code for?
Lactose permease (enzyme)
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What happens to the lac operon when lactose is absent from the growth medium?
Regulator gene (I) expressed, repressor protein synthesised, binds to O, covers part of P, RNA polymerase can't attach to P like normal, structural genes can't be transcribed to mRNA, the 2 enzymes (B-gal and lac. perm) can't be made
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What happens to the lac operon when lactose is added to the growth medium?
Lactose binds to rep. protein, shape changes, can't bind to O/dissociates from O, RNA polymerase binds to P, transcribes Z and Y, 2 enzymes made, bacteria can take up lactose into their cells, lactose converted to glucose, respiration
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In the lac operon, what does lactose act as once it is added to the growth medium?
An inducer
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Where does the lactose bind to once it is added to the growth medium?
The other side of the repressor protein, causing it to change shape
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What does the enzyme B-galactosidase do?
Catalyses the hydrolysis of lactose to glucose and galactose
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What does the enzyme lactose permease do?
Transports lactose into the bacterial cell
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What is a body plan?
The general structure of an organism
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What is the body plan controlled by?
Proteins coded for by homeotic genes
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How do homeotic genes control development?
They have regions called homeobox sequences that code for a part of the protein (the homeodomain), homeodomain binds to specific sites on the DNA, protein works as a transcription factor, activates/represses transcription, alters protein production
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Define apoptosis
Programmed cell death
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Describe the process of apoptosis
Cell produces enzymes, enzymes break down important cell components, cell shrinks, breaks up into fragments, fragments engulfed by phagocytes and digested
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How is apoptosis involved the the development of body plans?
Mitosis creates the bulk of body parts but apoptosis refines the parts by removing unwanted structures - separates digits, removes tadpoles tail cells, removes excess nerve cells
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What happens when a protein produced by protein synthesis isn't active?
It has to be activated by a molecule
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What molecules activate proteins?
Hormones, sugars
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How do the molecules activate proteins?
They work by binding to cell membranes and triggering the production of cAMP inside the cell, cAMP alters 3D shape of protein, protein is activated
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What does cAMP stand for?
Cyclic AMP
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What is cAMP and what does it do?
A secondary messenger - it relays the message from the contol molecule (ie. the hormone) to the inside of the cell
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What protein is activated by cAMP (example)?
Protein kinase A (PKA)
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How does cAMP activate PKA?
PKA is an enzyme with 4 units, cAMPT binds, causes a change in enzyme's 3D structure, releases the subunits that were originally bound together and inactive, subunits now active, PKA now active
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Define mutation
Any change to the base (nucleotide) sequence of DNA
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How many 'types' of mutation are there?
5
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Name the 5 types of mutation
Substitution, deletion, insertion, duplication, inversion
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Describe a substitution mutation
One base is swapped for another
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Describe a deletion mutation
One base is removed
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Describe an insertion mutation
One base is added
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Describe a duplication mutation
One or more bases are repeated
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Describe an inversion mutation
A sequence of bases is reversed
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How may a mutation affect an enzyme?
Primary structure altered, may change final 3D shape, protein (enzyme) doesn't work porperly, active sites may not form properly, substrates can't bind to the active sites
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What 3 effects may a mutation have?
Neutral, beneficial or harmful
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What are the ways that a mutation can have a neutral effect on a protein's function?
Amino coded for doesn't change (more than 1 triplet code per mutation), different amino coded for that's chemically similar to the original so it functions like the original, coded for amino not involved in protein's function (eg. far away from AS)
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What are the differences between neutral and beneficial/harmful mutations?
Neutral mutations won't affect an organism overall, beneficial and harmful mutations affect a protein's function - making it more or less active, effect on whole organism
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What is a beneficial mutation?
A mutation that has advantageous effects on an organism, increasing its chances of survival
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What is an example of a beneficial mutation?
Genes in a bacteria mutated so they code for an enzyme that breaks down an antibiotic
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What is a harmful mutation?
A mutation that has disadvantageous effects on an organism, decreasing its chances of survival
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What is an example of a harmful mutation?
Cystic fibrosis - deletion of 3 bases in the gene that codes for the CFTR protein) so the mutated protein folds incorrectly so it's broken down - leads to excess mucus production, affecting the person's lungs
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