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Flashcards in Nucleotides Deck (34)
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C, H, O, N, P






nucleic acids, polynucleotides such as DNA, RNA


general nucleotide structure

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DNA structure

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RNA structure

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What is a purine and pyrimidine?

2 types of bases: purine and pyrimidine
- purine bases have 2 carbon-nitrogen rings joined together
- pyrmidine bases have 1 carbon-nitrogen ring and is smaller than a purine base


purine bases and pyrimidine bases?

purine= adenine, guanine
pyrimidine= cytosine, thymine and uracil


differences between DNA and RNA?

- DNA has deoxyribose sugar, A/T/C/G bases
- RNA has ribose sugar, A/U/C/G bases
- DNA has 2 polynucleotide chains
- RNA has 1 polynucleotide chain


What is ADP and ATP?

- ADP and ATP are phosphorylated nucleotides
- phosphorylated nucleotides mean they have 1 or more phosphate groups added to it
- ADP (adenosine diphosphate) - adenine base, 2 phosphates, ribose sugar
- ATP (adenosine triphosphate) - adenine bases, 3 phosphates, ribose sugar


ADP to ATP and revers?

- plant and animal cells release energy from glucose (respiration)
- cells cant get energy directly from glucose so energy released from the breakdown of glucose in respiration is used to make ATP
- ATP is synthesised from ADP + inorganic phosphate ion
- ADP is phosphorylated to form ATP and a phosphate bond
- energy is stored in phosphate bond
- when energy is needed by the cell, ATP is broken down into ADP _ inorganic phosphate ion
- energy released from phosphate bond being broken is used by the cell


How do nucleotides join?

- they join between the phosphate group of one nucleotide and the sugar of another nucleotide
- joined by a phosphodiester bond (consist of a phosphate group and 2 ester bonds)


What is a sugar-phosphate backbone?

- a chain of sugars and phosphates


structure of a single polynucleotide strand

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DNA structure

- 2 DNA polynucleotide strands join by hydrogen bonding between bases
- each base can only pair with a particular base ( complementary base pairing
- a purine base always pairs with a pyrimidine
- 2 Hydrogen bonds form between A and T
- 3 Hydrogen bonds form between C and G
- 2 antiparallel polynucleotide strands twist to from DNA double-helix.


Purifying DNA using precipitation reaction

- break up cells in sample (using blender)
- make a solution of detergent (dilute washing up liquid), slat (sodium chloride) and distilled water
- add broken up cells to detergent solution
- incubate beaker in water bath at 60°C for 15 min
- put mixture into an ice bath to cool it down
- once cooled, filter mixture and transfer sample into boiling tube.
- add protease enzymes to filtered mixture to breakdown some protein in mixture
e.g. proteins bound to DNA. adding RNase enzymes will break down any RNA in mixture
- slowly dribble some cold ethanol down the side of tube to form a layer on top of DNA-detergent mixture
- DNA will form a white precipitate if left for a few minutes and remove from the tube using a glass rod.


what is the purpose of detergent in purifying DNA precipitation reaction?

detergent in mixture breaks down cell membranes. salt binds to DNA causing it to clump together. the temperature of the water bath should stop enzymes in cells form working properly and breaking down the DNA.


Explain what happens in semi-conservative DNA replication.

- DNA Helicase breaks H bonds between bases causing double helix to unzip forming to single separate strands
- each original single strand acts as template for new strand. Free-floating DNA nucleotides join to exposed bases on template strand by complementary base pairing (a-t, c-g)
- DNA Polymerase joins nucleotides on new strand together forming sugar-phosphate backbone. H bonds form between bases on original strand and new strand.
- strands twist to form double helix.


What is meant by semi-conservative DNA replication?

DNA replication is semi-conservative because each new DNA molecule contains one strand from original DNA and new strand


Accuracy and important of DNA replication

- has to be accurate to make sure genetic information is conserved each time DNA in cells is replicated
- random, spontaneous mutations occur often


what is a mutation?

a mutation is any change to the DNA base sequence and can alter the sequence of amino acids in a protein


What is a gene?

a gene is a sequence of DNA nucleotides that codes for a polypeptide
- the order of nucleotide bases in a gene determines the order of amino acids in a protein
- each amino acid is coded for by a sequence of 3 bases (triplet) in a gene


what is a genetic code?

- a genetic code is the sequence of base triplets (codon) in DNA/mRNA which codes for specific amino acids


What is a codon?

sequence of base triplets
3 adjacent bases


Non-overlapping genetic code

because base triplets don't share bases.
each base triplet is read in sequence, separate from the base triplet before and after it


degenerate genetic code

there are more possible combinations of triplets than there are amino acids.
means some amino acids are coded for by more than one base triplet


universal genetic code

same specific base triplets code for same amino acids in all living things


start/end triplets

some triplets are used to tell the cell to start/stop protein production
called start/stop codon and are found at the beginning/end of a gene



- RNA polymerase attaches to DNA double helix at beginning of a gene causing H bonds between the two DNA strands to break (in a gene) which separates the strands and DNA uncoils at that point. One of the strand is used as anti-sense/template strand to make an mRNA copy.
- RNA Polymerase lines up free RNA nucleotides alongside template strand. Complementary base pairing means mRNA strand ends up being a complementary copy of DNA template strand (except base T is replaced by base U in RNA). Once all nucleotides have paired up with their specific base on DNA strand, they are joined together forming an mRNA molecule.
- RNA Polymerase moves along DNA strand, separating the strands and assembling the mRNA strand. H bonds between uncoiled strands of DNA re-form once RNA Polymerase has passed by allowing the strands to coil back into double-helix.
- when RNA Polymerase reaches a stop codon, it stops making mRNA and detaches from DNA. mRNA moves out of nucleus through a nuclear pore and attaches to a ribosome in cytoplasm ready for translation.



- mRNA attaches itself to ribosome and tRNA molecules carry amino acids to ribosome.
- a tRNA molecule with an anticodon that's complementary to start codon on mRNA attaches itself to mRNA by complementary base pairing. A second tRNA molecule attaches itself to next codon on mRNA in same way
- rRNA in ribosome catalyses formation of peptide bonds between the 2 amino acids attached to the tRNA molecules joining the amino acids together. The first tRNA molecule move away leaving the amino acid behind.
- third tRNA molecule binds to next codon on mRNA. its amino acids binds to the first 2 and the second tRNA molecule moves away. This process continues, producing a chain of linked amino acids (a polypeptide chain) until a stop codon has been reached on mRNA molecule.
- polypeptide chain moves away from ribosome and translation is complete.