2.1.3 Nucleotides and nucleic acids Flashcards
structure of nucleotide
monomer that makes up nucleic acids when joined by phosphodiester bonds
ribose (pentose sugar)
phosphate group (phosphodiester bond with 5 carbon of ribose)
nitrogenous base (phosphodiester bond with 1 carbon of ribose)
ADP and ATP structure
phosphorylated nucleotides
ADP = 1 additional phosphate group
ATP = 2 additional phosphate group
how nucleic acids / polynucleotides form
condensation reactions to form phosphodiester bonds
between OH group on 3 carbon of pentose sugar and phosphate group on 5 carbon of pentose sugar of another nucleotide
forms sugar phosphate backbone
complementary base pairs of nucleotides
adenine+thymine (uracil in RNA), 2 hydrogen bonds
cytosine+guanine, 3 hydrogen bonds
pyrimidines
smaller bases
single carbon ring structure
thymine, cytosine
purines
larger bases
double carbon ring structure
adenine, guanine
DNA molecule structure
2 polynucleotides coiled into DNA double helix
sugar phosphate backbone
2 strands held together by hydrogen bonds between complementary base pairs
strands have 3’ (hydroxyl group) and 5’ (phosphate group) ends
strand run anti parallel (parallel and in opposite directions)
RNA structure
single strand
uracil instead of thymine
ribose sugar instead of deoxyribose sugar in DNA
DNA extraction method (plant cells)
grind sample with pestle and mortar (break down cell wall)
mix sample with detergent (break down cell membrane)
add salt (breaks hydrogen bonds between DNA and water)
add protease enzyme (breaks down histones associated with DNA)
add ethanol on top of sample (DNA precipitates out of solution)
“spool” DNA (white strands) using glass rod
why DNA replication is semi-conservative
2 molecules of DNA produced each time
both consisting of one original strand and one new strand
DNA replication method
occurs during synthesis phase of interphase gyrase unwinds double helix
DNA helicase catalysing break down of hydrogen bonds between complementary nitrogenous base pairs and “unzips” double helix
free DNA nucleotides pair with exposed bases of template strand
DNA polymerase catalyses formation of phosphodiester bonds between nucleotides (builds from 5’ to 3’)
leading strand is continuous
lagging strand is discontinuous and forms Okazaki fragments
DNA ligase catalyses joining of Okazaki fragments
mutation definition
random and spontaneous errors in the sequence of bases that occur during replication
why DNA is genetic code
DNA codes for sequences of amino acids that form different proteins for organism
different proteins are foundation of physical and biochemical characteristics of organisms
codon definition
triplet code (3 nitrogenous bases in a row) codes for an amino acid
gene definition
section of DNA consisting of complete sequence of codons to code for a protein
roles of different codons
start codon: if at beginning of gene, signalling start of sequence that codes for a protein
“stop” codons: 3 of them, don’t code for any amino acids, signal end of sequence
if start codon is in middle of gene, it codes for amino acid methionine
why genetic code is non-overlapping
start codon ensures codons are read “in frame” (in the right order) and won’t overlap with other genes
why code is degenerate
many amino acids can be coded by more than one codon
high likelihood that mutation won’t alter sequence of amino acids
transcription method
gyrase unwinds double helix
RNA polymerase catalyses break down of hydrogen bonds between complementary nitrogenous base pairs, “unzips double helix”
free RNA nucleotides form hydrogen bonds with exposed complementary bases on template strand
RNA polymerase catalyses formation of phosphodiester bonds between nucleotides
transcription stops at end of gene, mRNA is formed, detached from template strand and leaves through nuclear envelope to ribosome
DNA double helix reformed
strands in transcription
sense strand: 5’ to 3’, codes for protein
antisense strand: 3’ to 5’, complementary to sense strand, template strand in transcription
RNA uses antisense strand as a template so has same sequence as sense strand
ribosome structure
large and small subunits
made up of protein, ribosomal RNA, site that catalyses formation of peptide bonds
tRNA structure
strand of RNA
folded so 3 bases (anticodon) exposed at one end of molecule so can bind to complementary codon on mRNA
carries corresponding amino acid
translation method
mRNA binds to small subunit of ribosome at start codon (AUG)
tRNA with complementary anticodon and corresponding amino acid binds to mRNA start codon
another tRNA binds to next codon on mRNA
peptide bond form between amino acids on 2 tRNA (catalysed by peptidyl transferase)
ribosome moves along mRNA, releasing first tRNA, peptide chain begins to peel away from ribosome and fold into protein
repeat until at stop codon
ribosome falls apart, releasing finishes protein
how multiple identical polypeptides can be made quickly
polysome
many ribosomes can follow on mRNA behind the first
multiple identical polypeptides can be synthesised simultaneously
enzyme in translation
peptidyl transferase
