Nucleic Acids and their functions

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What does a nucleotide consist of?
A nucleotide consists of three sub-units, a 5 carbon sugar, a base that contains nitrogen and a phosphate group
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What does ATP stand for?
Adenosine Triphosphate
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What does ATP consist of?
A pentose sugar, a base (adenine) and three phosphate groups
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What type of cellular activities use ATP?
Active transport, Cell division, muscle contraction
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What is an energy yielding reaction called?
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What is an energy requiring reaction called?
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What 2 things are ATP formed from?
Adenosine diphosphate and an inorganic phosphate ion
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What is the name of the enzyme that catalyses the reaction for the formation of ATP?
ATP synthetase
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What is the equation for ATP synthesis and what is the reaction known as?
ADP + Pi (+ATP Synthetase) ----> ATP + H2O
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Why is ATP described as being universal?
It supplies energy for nearly every reaction and in all organisms
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What is the difference between ribose and deoxyribose when it comes to the structure of the pentose?
The oxygen atom has been removed from carbon 2 in deoxyribose (Hence the name DEoxy)
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For are the 4 different nucleotide bases in DNA?
Adenine, thymine, cytosine and guanine
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What is the differences between the 4 bases in DNA than in RNA?
The only difference is that RNA doesn't have thymine but has Uracil instead
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What are adenine and guanine?
Purine bases
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What are cytosine and thymine?
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How are the components of nucleotides linked together?
Condensation reactions
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What and how is formed when two nucleotides join together?
A dinucleotide, condensation reaction between the phosphate group of one nucleotide and the thrid carbon of the pentose sugar of the other nucleotide
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What is formed when millions of nucleotides join together?
A polynucleotide or a nucleic acid
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What is the nucleic acid said to have in relation to it's structure?
A sugar-phosphate backbone
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What links are in the sugar phosphate backbone?
Strong covalent bonds
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What does DNA consist of?
Two polynucleotide chains that run antiparallel.
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What joins the opposite complementary bases of the two polynucleotide chains?
Hydrogen bonds, 3 bonds between cytosine and guanine, 2 between adenine and thymine
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How is the twisted shape of the DNA molecule described as?
A double helix
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Who made a model for the structure of DNA in 1953?
James Watson and Francis Crick
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In what 3 ways is RNA different to DNA?
RNA is made up of only 1 polynucleotide chain, The pentose sugar is ribose, the pyrimidine base uracil is present in some of its bases not thymine
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What are the 3 different forms of RNA?
mRNA (messenger RNA), tRNA (Transfer RNA), rRNA (Ribosomal RNA)
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What is the function of DNA?
DNA is needed for replication and it holds the genetic code which codes for the production of proteins
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At the start of replication, what is the enzyme that unwinds the DNA molecule and breaks the hydrogen bonds?
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What happens after the helicase has done it's job?
The 2 strands act as templates to which free DNA nucleotides can attach via base pairing (A-T and C-G)
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How do the free nucleotides link together?
Via condensation reactions
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What is the name of the enzyme that inserts and links the free DNA nucleotides together?
DNA Polymerase
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What happens after DNA polymerase has done it's job?
Hydrogen bonds form between the two new polynucleotide chains and the strands twist into a new helix
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Each of the new DNA molecule has 1 original strand and 1 new strand, what is this process said to be called?
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What else does DNA replication require?
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Who conducted the experiments that for provided the evidence for semi conservative replication?
Meselson and Stahl
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What type of bacteria did they use in their experiments?
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Why did they use bacteria in their experiments?
They are prokaryotes and so have no nuclear membrane, the DNA is 'naked' in the cell and there for easier to extract, it's relatively easy to culture bacteria and their numbers double every 20-30mins
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Explain what Meselson and Stahl did before the experiment and explain the results they got.
Before the experiment they broke open E.Coli cells, extracted DNA and the DNA was centrifgued. There was a band of normal or "Light" DNA high up in the centrifuge tube.
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To start their experiment what did Meselson and Stahl do?
They cultured E.Coli in a growth medium containing an isotope of N15.
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How many generations was the E.Coli allowed to grow in the N15 medium?
Many generations so that all nitrogen in every E.Coli was N15 not N14
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After the E.Coli was cultured in the N15 medium, what was done next?
E.Coli with N15 was broken open, DNA extracted + Centrifuged.
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When they centrifuged the N15 DNA, what were their results?
There was a band low down in the tube of "Heavy" DNA
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What was done after centrifuging the N15 E.Coli?
They took a sample of the E.Coli labelled with N15, washed it and re suspended in a new growth medium containing N14
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Why was the N15 E.Coli washed before further use?
To remove the N15 medium on the outside
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For how long was the N15 E.Coli allowed to divide in the N14 medium?
One generation only
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After being allowed to divide for one generation only, what was then done to the E.Coli?
They were broken open, DNA extracted and centrifuged
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What was the results after centrifuging the 15N suspended in N14?
The DNA band was at an indeterminate position on the centrifuge tube, this means the DNA has 1 new light strand and one old heavy strand.
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In order to make the semi-conservative experiment a fair test, what should be done?
The centrifuge tube should be spun at the same speed, The DNA sample should be spun for the same time, the gel in the tube should be of the same density
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What is a gene?
The sequence of bases in a single gene determines the order that the amino acids are assembled into in a polypeptide chain
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How many amino acids are there?
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Why can't 1 base code for the production of 1 amino acid?
Because if that was the case there would only be 4 amino acids because there's only 4 bases
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Why can't 2 bases code for the production of 1 amino acid?
That would only result in 16 combinations and there are 20 amino acids.
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How many bases code for 1 amino acid and why?
3, because this means a total of 64 combinations are possible which is more than enough for the 20 amino acids that exist.
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What is a triplet of bases called?
A codon
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Due to 64 possible combinations, what does this tell us?
Every amino acid has more than 1 codon
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Out of the 64 combinations, how may code for amino acids and what are the others for?
61, the other 3 are start and stop codons which tell the cell when to start and stop reading the code
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What are start and stop codons also called?
Degenerate or redundant
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Why are codons universal?
A codon always codes for the same amino acid in any organism
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What are exons?
Regions of DNA that contain the code for proteins
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What are introns?
Regions of non-coding DNA
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Why does transcription take place?
The DNA is confined to the chromosomes in the nucleus and protein synthesis takes place in ribosomes in cytoplasm, therefore the code has to be read and copied into another molecule
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What is the messenger molecule in transcription called?
mRNA ( Messenger RNA)
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What is the enzyme that starts transcription?
RNA Polymerase
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What is the start codon for every gene?
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What does RNA polymerase do?
It breaks the hydrogen bonds binding the two DNA strands and exposes the bases
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After RNA polymerase has broken the H bonds, what happens next?
Free RNA nucleotides align themselves opposite complementary bases of 1 strand only!
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After the RNA nucleotides have aligned themselves, what happens next?
Condensation reactions link them together to give a molecule of mRNA, this peels off the DNA and leaves the nucleus via the nuclear pore
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What is translation?
Translation is the synthesis of a polypeptide chain by the ribosomes using the genetic code on the mRNA to put to amino acids in the correct sequence
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What is the shape of tRNA describe as?
A cloverleaf shape
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What is the function of tRNA?
To serve as a link between the amino acids and the mRNA
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What is on the tRNA molecule which determines the amino acid it brings to the ribosomes?
It has an anti-codon
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What are ribosomes composed of?
Equal mixture of protein and rRNA
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What is the function of a ribosome?
To hold the mRNA, tRNA and amino acids steady so a polypeptide can be assembled
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Where is rRNA made?
In the nucleolus of the the nucleus
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What happens at the start of translation?
The small sub-unit of the ribosome binds to the mRNA at the start codon and is then joined by the large sub-unit with a tRNA molecule attached.
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How many codons does the ribosome cover at once?
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What determines what tRNA molecule is brought to the ribosome?
The complementary anti-codon it has to the codons on the mRNA molecule
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When 2 amino acids are along side each other what forms between them?
A peptide bond
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What is needed for peptide bond formation?
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What happens to a tRNA molecule leaves the ribosome after delivering the right amino acid?
It picks up the same amino acid as determined by its anti-codon
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What happens when the ribosome reaches the stop codon?
The two sub units separate, the polypeptide chain is released and the process can start again.
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What is it called when multiple ribosomes move along the mRNA at the same time?
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Where does further modification of proteins take place?
The golgi body
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What do modifications of proteins include?
The association of 2 or more PP chains to form a quaternary structure, the joining of PP chains with non-protein components
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What is a change in a base sequence called?
A mutation
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What happens when a mutation occurs?
A different amino acid is likely to be added to the PP chain during translation, this would change the primary structure of the PP, this causes a change in the tertiary structure and could result in a non functioning protein
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Card 5


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