Nucleic acids Flashcards
what is the structure of nucleotides?
- monomers from which nuclei acids are made
describe the differences between DNA and RNA nucleotides?
- pentose sugar: deoxyribose in DNA and ribose in RNA
- Bases: adenine, thymine, guanine and cytosine in DNA, adenine, guanine, uracil and cytosine.
-mainly involved in: storage of genetic information for DNA, protein synthesis for RNA.
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what are purines?
Bases with a double-ring structure e.g. adenine and guanine
what are pyrimidines?
bases with a single-ring structure e.g. thymine and cytosine
the structure of DNA
- Consists of two polynucleotide strands (the back bone) that are anti-parallel (in opposite directions)
- complementary base pairs in the centre held by hydrogen bonds
- C and G form 3 hydrogen bonds
-A and T form 2hydrogen bonds - proportion of A and T and G and C are the same
how are polynucleotides formed?
when a phosphodiester bond is formed in a condensation reaction between the phosphate group of one nucleotide and the the hydroxyl group on the pentose sugar of the other nucleotide
structure of ADP and ATP
phosphorylated nucleotides meaning they contain more than one phosphate group so are comprised of a pentose sugar (ribose), a nitrogenous base (adenine) and inorganic phosphates.
describe how DNA replicates?
- DNA helicase uncoils the structure the double helix structure by breaking the hydrogen bonds between the strands
-each strand act as a template - free nucleotides from the cytoplasm joins to the template in complementary base pairs
- DNA polymerase joins the the nucleotides forming phosphodiester bonds forming a new sugar-phosphate backbone
-semi-conservative replication
describe the practical investigations into the purification of DNA
- first crush the piece of fruit using a pestle and mortar this help break down the cellulose cell wall
-add detergent this dissolves the cell surface membrane
-add protease enzyme which break down the histogram proteins associated with DNA
-filter to remove solids - add salt to help the DNA clump together
-pour cold alcohol into the mixture as DNA is insoluable in alcohol so should float to the top of
genes
- a section of DNA that codes for the sequence of amino acids in a polypeptide
the nature of the genetic code
- near universal: in almost all living organisms the same triplet of DNA bases codes for the same amino acids
- degenerate: for all amino acids except methionine and tryptophan, there is more than one base triplet which can code for the base this reduce the effect of mutations as a change is one base of triplets could produce another base triplet that still codes for the same amino acids
- non-overlapping: each triplet is not read more than once
transcription
the process of making MRNA from a DNA template
describe the process of transcription
- DNA helicase breaks the hydrogen bonds between the strands
- complementary RNA nucleotides join with the bases of the exposed nucleotides
- the mRNA molecule is a copy of DNA strand
-RNA polymerase joins the RNA nucleotides forming phosphodiester bonds. - MRNA is produced and moves out of the nucleus through the nuclear pore
codon
A sequence of three bases (triplets) on mRNA that codes for a specific amino acid.
translation
the formation of a protein, at ribosomes
describe the stages of translation
- MRNA attaches to a ribosome that is made up of two subunits of rRNA
- TRNA molecule with a anticodon complementary to the start codon attaches binds to the MRNA by complementary base pairing
- another tRNA molecule attaches itself to the next codon on the MRNA.
- peptide bond is formed between the amino acids on the first and second tRNA molecule catalysed by an enzyme
- the first tRNA molecule moves away leaving the amino acid behind
- a third tRNA molecule binds to the next codon and its amino acid binds to the first 2. the 2nd tRNA molecule moves away
- process of ribosome moving along the mRNA continues producing a polypeptide chain. until stop codon is reached
- polypeptide chain moves away from the ribosome
evidence for semi-conservative replication
- scientist in 1958 grew ecoli in N15. most of DNA in the bacteria was heavy
- then transferred the bacteria into a medium containing N14 and was left for long enough to undergo one replication, from this a hybrid DNA was produced.
- Bacteria divided once more this produced one hybrid strand and one light showing DNA is semi-conservative,
why is it important that DNA replication is accurate?
- to make sure the genetic information is conserved each time the DNA is replicated
Why is DNA replication considered semi- conservative
The new DNA molecule contains one strand of the original DNA and one strand of the new DNA. The original strand acts as a template for new strands
What is a allele
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Different versions of a gene
