1.5 Nucleic acids Flashcards
what are the monomers of nucleic acids?
nucleotides
state the three components of nucleotides.
pentose sugar
organic base
phosphate group
what are the two types of organic base?
purine and pyrimidine
what is a purine?
class of organic bases
double ring structure
includes adenine (A) and guanine (G)
what is a pyrimidine?
class of organic bases
single ring structure
includes cytosine (C), thymine (T), uracil (U)
describe the structure of a DNA nucleotide.
deoxyribose
organic base (A, T, C or G)
phosphate group
describe the structure of an RNA nucleotide
Ribose
organic base (A, U, C or G)
phosphate group
describe the structure of an ATP nucleotide.
Ribose
Adenine
three phosphate groups
what is an endergonic reaction?
a non-spontaneous reaction that requires an input of energy, e.g. ATP formation.
what is an exergonic reaction?
a spontaneous reaction that overall releases energy, e.g. ATP hydrolysis
describe the role of ATP
Universal Energy Currency. Hydrolysed to release energy:
ATP + Water ⇌ ADP + Pi + Energy
what is complementary base pairing?
describes how hydrogen bonds form between complimentary purine and pyrimidine bases
two bonds form between A and T (or U)
three bonds form between G and C
describe the structure of DNA
Double-stranded polymer of nucleotides twisted to form a double helix
nucleotides joined by phosphodiester bonds
hydrogen bonds form between complementary base pairs, A and T, C and G
anti parallel strands
describe the structure of RNA
single-stranded polymer of nucleotides
nucleotides joined by phosphodiester bonds
hydrogen bonds form between complementary base pairs, A and U, C and G
compare and contrast DNA and RNA
DNA/RNA
double stranded/ single stranded
long chain of nucleotides/ short chain of nucleotides
contains deoxyribose sugar/ contains ribose sugar
contains bases A, T, C, G/ contains bases A, U, C, G
storage of genetic info/ role in protein synthesis
both phosphodiester bonds to join nucleotides
name the 3 types of RNA found in cells
transfer RNA (tRNA)
messenger RNA (mRNA)
ribosomal RNA (rRNA)
what is the function of tRNA?
it carries specific amino acids to the ribosomes
describe the structure of tRNA.
80 nucleotides
single helix
clover leaf shape
anticodon on one end, amino acid binding site on the other
what is the function of mRNA?
carries genetic information from the nucleus to the ribosomes for protein synthesis.
describe the structure of mRNA
2000 nucleotides
single helix
unstable
what is the function of rRNA?
associates with proteins in the cytoplasm to form ribosomes.
what is the structure of rRNA?
1800 to 5000 nucleotides
two subunits: one large, one small
what is semi-conservative replication?
the replication of DNA to produce two new DNA molecules which both contain one new strand and one old strand from the original DNA molecule.
what is the role of DNA helicase in semi-conservative
it catalyses the unzipping of double-stranded DNA into two single strands, each of which acts as a template
what is the role of DNA polymerase in semi-conservative replication?
it catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand.
what is the genetic code?
the rules which triplets in a DNA base sequence code for the sequence of amino acids in a polypeptide chain. The genetic code is degenerate, universal and non-overlapping.
why is the genetic code described as degenerate?
more than one triplet can code for a particular amino acid.
why is the genetic code described as universal?
the same codons code for the same amino acids in almost all organisms.
what is meant by ‘non-overlapping’?
each base in a sequence is read once and is only part of one triplet.
describe the ‘triplet code’ for amino acids.
a specific sequence of three nucleotides (known as a codon) on a molecule of DNA or RNA codes for a particular amino acid in protein synthesis.
what is an exon?
a region of DNA that codes for an amino acid sequence
what is an intron?
a non-coding sequence of DNA that is found between exons.
compare eukaryotic and prokaryotic genes.
eukaryotic genes are discontinuous with non-coding introns and coding exons
prokaryotic genes are continuous with coding sequences only
what is protein synthesis?
the formation of proteins from amino acids. There are two stages:
transcription and translation
describe transcription
first stage of protein synthesis
the formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA
outline the process of transcription.
DNA helicase unwinds section of DNA, breaking hydrogen bonds between the DNA strands. Antisense strands act as a template.
RNA polymerasae bonds to promoter region on a gene
Free RNA nucleotides align next to their complimentary bases
RNA polymerase joins adjacent RNA nucleotides, forming phosphodiester bonds
RNA polymerase reaches stop codon and detaches. mRNA complete.
describe post-transcriptional modification
splicing removes introns from pre-mRNA in eukaryotic cells
define translation
second stage of protein synthesis
takes place in the ribosomes
mRNA used as a template for the attachment of tRNA molecules with complementary anticodons. Amino acids carried of adjacent tRNA molecules are joined to form a polypeptide chain.
outline the process of translation.
mRNA attaches to groove between subunits of ribosome
Ribosome moves along mRNA until ‘start’ codon reached
Amino acid-tRNA complex anticodon attaches to complementary mRNA codon via hydrogen bonding. Another complex binds
Peptide bond forms between adjacent amino acid in the complexes
Ribosome moves along one codon and release empty tRNA. Process continued to form polypeptide chain until ‘stop’ codon is reached.
what is the ‘one gene - one polypeptide’ hypothesis?
the theory that each gene encodes a single protein
what happens to the polypeptide after translation?
further modified by adding carbohydrates, lipids or phosphates.
Different polypeptides may be combined
describe how DNA can be purified by precipitation.
Add ethanol and a salt to aqueous solution. Nucleic acids precipitate out of solution.
Centrifuge to obtain pellet of nucleic acid.
Wash pellet with ethanol and centrifuge again.
Why are strawberries selected for this practical?
They have a large genome.
They are soft and hence can be broken down easily.
What is the purpose of adding washing-up liquid?
To break down the phospholipid membranes.
Why is pineapple juice added?
Pineapple juice contains proteases to digest proteins in cells.
Why is salt added?
To neutralise the negative charge of the phosphates in DNA, hence lowering its solubility to be precipitated out.
Why is the mixture heated at 60°C?
To speed up the rate of reaction of the proteases in pineapple, so cell proteins are digested at a faster rate.
Why is iced ethanol added?
The solubility of DNA is lower in ethanol and in cold temperatures, hence this allows DNA to be precipitated out.
