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48 Cards in this Set
- Front
- Back
What does DNA stand for?
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Deoxyribose nucleic acid
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What does RNA strand for?
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Ribonucleic acid
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What is the difference between DNA and RNA
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DNA contains deoxyribose sugar, RNA contains ribose sugar
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What is the monomer of polynucleotides?
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Nucleotides
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Describe the structure of a nucleotide?
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Made up of 3 parts 1. A phosphate group 2. A pentose sugar 3. An organic nitrogenous base |
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How are the 3 parts of nucleotides joined together?
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By covalent bonds formed in condensation reactions
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What bases are found in DNA
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ATCG (Adenine, Thymine, Cytosine, Guanine)
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What bases are found in RNA?
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AUCG (Adenine, Uracil, Cytosine, Guanine)
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What is the structure of purine bases
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have 2 rings
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What is the structure of pyrimidine bases
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Have one rine
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Which bases are purine?
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Adenine, Guanine
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Which bases are pyrimidine
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Cytosine, Thymine, Uracil
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What bond is formed between nucleotides?
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A phosphodiester bond
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Describe the structure of DNA
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2 polynucleotide chains in antiparallel joined in a double helix structure.
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How are the chains in DNA held together?
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With hydrogen bonds formed via complementary base pairing (AT and CG)
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How many hydrogen bonds form between A and T?
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2
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How many hydrogen bonds form between C and G?
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3
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What 5 functions of DNA are caused by its structure?
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The sequence of bases is a code to build proteins. Each long molecule stores lots of information. The complementary base pairs can be replaced and easily copies. Double helix gives the molecule stability. Hydrogen bonds allow for easy unzipping for copying and reading information. |
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What is a triplet code and what does it do?
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3 bases code for 1 amino acid
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Where does DNA replication begin
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At a replication fork (where two strands open and separate)
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What name is given to the process whereby DNA replicates?
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Semiconservative replication
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What is the combination of new or old strands in the daughter helix?
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Made up of 1 original strand and one newly synthesised strand
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Who proved the hypothesis of semiconservative replication?
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Meselsohn and Stahl
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What is the role of DNA gyrase in the first step of DNA replication?
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DNA gyrase uncoils the double helix to create a straight ladder like shape
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What is the role of DNA helicase in the second step of DNA replication?
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DNA helicase breaks the weak hydrogen bonds between complementary bases and strands separate at replication fork.
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What is the role of DNA polymerase in the 3rd step of DNA replication.
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DNA polymerase adds new ATP activated nucleotides to the exposed bases using complementary base pairing
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How does complementary base pairing occur on the lagging strand during DNA replication?
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in Okazaki fragments
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What is the function of DNA ligase in the 4th stage of DNA replication?
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DNA ligase helps join segments together by recreating the sugar phosphate backbone by recreating phosphodiester bonds between nucleotides
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What is the role of DNA polymerase at the same time as DNA ligase is functioning in the 4th stage of DNA replication?
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DNA polymerase proofreads the new DNA, checking for errors and repairing them, this is called excision repair.
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What is the role of DNA helicase in the final stage of DNA replication?
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DNA helicase recoils the 2, new identical DNA molecules which each consist of 1 old strand and 1 new strand
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How is DNA organised in eukaryotes
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Highly coiled and folded into chromosomes The proteins around which DNA is coiled are Histone proteins Loops of DNA can also be found in mitochondria |
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How is DNA organised in prokaryotes
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DNA forms a long molecule in a complete circle there are no histones Prokaryotic cells can also contain plasmids |
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What did Meselsohn and Stahl prove?
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Semiconservative replication
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They grew E.coli in heavy and light isotopes of what element?
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Nitrogen (N15 and N14)
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What are the two stages of protein synthesis?
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Transcription and translation
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Where does transcription take place?
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In the nucleus
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What enzyme is involved in transcription?
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RNA polymerase
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What is the product of transcription?
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A single strand of mRNA
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How does the mRNA exit the nucleus?
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Via a nuclear pore
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Where does translation take place?
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In the cytoplasm
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What is a codon?
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Each 3 bases of mRNA
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How many mRNA bases are exposed at a time when a ribosome attaches to the mRNA?
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6
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What happens in translation after the ribosome has attached to the mRNA?
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tRNA with the correct anticodon, and a specific amino acid attached to it, complementary base pairs with the mRNA codon to bring the specific amino acid to the ribosome.
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How does translation allow a polypeptide chain to form?
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The amino acids, which were brought to the ribosome by the tRNA, join via peptide bonds to form the start of a polypeptide chain.
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What is the start codon?
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AUG
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How many stop codons are there?
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3
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What happens when a stop codon is reached?
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The ribosome stops translating
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What would happen if a mutation caused a stop codon to appear early?
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A truncated protein would be produced
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