DNA and nucleotides
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- Created by: Emily.T
- Created on: 19-12-17 17:54
What is a nucleotide?
A type of biological molecule that make up DNA and RNA
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What is a nucleotide made from?
A pentose sugar (sugar with 5 carbon atoms), a phosphate group and a nitrogenous base
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What does DNA stand for?
Deoxyribose nucleic acid
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What is DNA used for?
To store genetic information
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What is RNA used for?
To make proteins from the instructions in DNA
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What pentose sugar is in DNA?
Deoxyribose
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What are the four possible bases for DNA?
Adenine - Thymine - Cyotsine - Guamine (ATCG)
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What are purine bases?
A base that contains two carbon-nitrogen rings joined together
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What is a pyrimidine base?
A base that only has one carbon-nitrogenring
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What bases for DNA are a purine base?
Adenine and Guamine
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What bases for DNA are a pyridimine base?
Cytosine and Thymine
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What is the pentose sugar in RNA called?
Ribose
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What are the bases for RNA?
Adenine - Uracil - Cytosine - Guamine (AUCG)
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Is Uracil a purine base or a pyrimidine base?
Pyrimdine
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What are two (or more) nucleotides called when they are joined together?
Polynucleotides
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Where does the two nucleotides join?
Between the phosphate group of one nucleotide and the (pentose) sugar of another
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What type of bond is formed between two nucleotides?
Phosphodiester bond
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What is the name for the chain of sugars and phosphates?
Sugar-phosphate backbone
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What do two polynucleotides form when they join together?
A double-helix
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How do the two DNA polynucleotides join together?
By the hydrogen bonds between the bases
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What is complementary base pairing?
Where each base can only join with one particular base
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What base pairs with what base?
Adenine + Thymine (AT) - Cytosine + Guamine (CG)
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What base does Uracil bind with in RNA?
Adenine (as it replaces Thymine)
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How many hydrogen bonds form between Adenine and Thymine?
2
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How many hydrogen bonds form between Cytosine and Gumaine?
3
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Are the two strandes of DNA that form the double helix parallel or antiparallel?
Antiparallel
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What is the first stage of DNA replication?
1) DNA helicase breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzips and unwinds to form two single strands.
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What is the second stage of DNA replication?
Each original single strand acts as a template for a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing (A+T) (C+G)
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What is the third stage of DNA replication?
The nucleotides of the new strand are joined tgether by DNA polymerase. This forms the sugar-phosphate backbone. Hydrogen bonds are form between bases on the original and new strand. The strands twist to form a double-helix.
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What is the fourth stage of DNA replication?
Each new DNA molecule contains one strand from the original DNA molecule and one new strand.
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What type of copying is this DNA replication and why?
Semi-conservative replication because half of the strands in each new DNA molecule are from the original piece of DNA and one from the new strand.
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What is mutation in DNA replication and what is their impact?
A mutations is any random and spontaneous change to the DNA base sequence. They don't always have an effect, but they can alter the sequence of amino acids in a protein which can cause an abnormal protein to be produced.
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What is a gene?
A sequence of DNA nucleotides that codes for a polypeptide.
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What determines the order of amino acids in a protein?
The order of nucleotide bases
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What codes an amino acid?
The sequence of three bases (aka a triplet) in a gene
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Where are DNA molecules found?
In the nucleus of the cell
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Why is DNA copied into RNA?
For protein synthesis as DNA is too large to move out of the nucleus, so a section is copied into mRNA in a process called transcription.
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Where does the mRNA go to after leaving the nucleus?
To join to the ribosomes in the cytoplasm to be used to synthesise a protein in a process called translation.
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How many types of RNA are there?
3
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Which base does Uracil pair with?
Adenine
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Messenger RNA: mRNA
1) Made in the nucleus 2) Three adjacent bases = codon 3) Carries 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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Transfer RNA: tRNA
1) Found in the cytoplasm 2) Has an amino acid binding site at one end & sequence of 3 bases at the other end called an anticodon 3) Carries the amino acids used to make proteins to the ribosomes during translation
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Ribosomal RNA: rRNA
1) Forms the two subunits in a ribosome 2) Ribosome moves along the mRNA strand during protein synthesis. rRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids
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What is the genetic code?
The sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids.
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How is the genetic code read?
Each base triplet is read in sequence, separate from the triplet before it and after it as base triplets don't share their bases - the code is non-overlapping
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What does it mean by the fact that the genetic code is degenerate?
That there are more possible combinations of triplets than there are amino acids
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How many amino acids and possible triplets are there?
Amino acids = 20 Triplets = 64
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What does it mean that the genetic code is degenerate?
That some amino acids are coded for by more than on base triplet
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What are stop and start codons?
A stop codon is a triplet that tells the cell when to stop the production of a protein. - A start codon tells the cell to start the production of a protien. They're found at the beginning and end of the gene.
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What does it mean that the genetic code is universal?
That the same specific base triplets code for the same amino acids in all living things.
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What is the first stage of protein synthesis?
Transcription
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What happens during transcription? 1
1) Starts when RNA polymerase attaches to the DNA double-helix at the start of a gene. 2) Hydrogen bonds the two DNA strands break, strands separate and DNA uncoils. 3) One original strand is used as a template to make an mRNA copy.
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What happens during transcription? 2
4) RNA polymerase lines up free nucleotides alongside the template strand. Complementary base pairing = mRNA strand is a complementary copy of the DNA template strand (but T is replaced with U).
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What happens during transciption? 3
5) RNA nucleotides pair up with their specific bases on DNA strand, forming an mRNA molecule 6) RNA polymerase moves along DNA, separating the strands & assembling mRNA strand 7) Hydrogen bonds strands reform and coil into double-helix
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What happens during transcription? 4
8) RNA polymerase reaches a stop codon so mRNA stops being made and detaches from the DNA 9) mRNA moves out of the nucleus through a nuclear pore & attaches to a ribosome in the cytoplasm, where translation takes place.
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What is the second stage of protein synthesis?
Translation
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Where does translation occur?
At the ribsomes in the cytoplasm
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What happens with amino acids during translation?
Amino acids are joined together to make a polypeptide chain, following the sequence of codons carried by the mRNA
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What happens during translation? 1
1) mRNA attaches to a ribosome and tRNA molecules carry amino acids to the ribosome 2) A tRNA molecule with a complementary anticodon to the start codon on the mRNA, attaches to the mRNA by complementary base pairing
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What happens during translation? 2
3) A second tRNA attaches to the next codon on the mRNA 4) rRNA catalyses the formation of a peptide bond two amino acids attached to tRNA joining the amino acids together. 1st tRNA mol moves away leaving its amino acid behind
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What happens during translation? 3
5) A 3rd tRNA binds to the next codon. Its amino acid binds to the first two & the second tRNA moves away to pick up another amino acid (recycle)
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What happens during translation? 4
6) This process continues, producing a chain of linked amino acids (polypeptide chain) until there's a stop codon on the mRNA 7) Polypeptide chain moves away from the ribosome and translation is complete.
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Other cards in this set
Card 2
Front
What is a nucleotide made from?
Back
A pentose sugar (sugar with 5 carbon atoms), a phosphate group and a nitrogenous base
Card 3
Front
What does DNA stand for?
Back
Card 4
Front
What is DNA used for?
Back
Card 5
Front
What is RNA used for?
Back
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