2.3 Nucleic Acid ✓

double helix

molecule consisting of a five-carbon sugar, phosphate group and nitrogenous base

large molecule containing many nucleotides

1

5 or 3

condensation reaction

nucleotides

ribose

deoxyribose

phosphorylated nucleotides

-ADP (adenosine diphosphate)
-ATP (adenosine triphosphate)

energy-rich end-product of energy releasing biochemical pathways, used to drive energy-requiring metabolic processes

by ATP, ADP, AMP

nucleotides

adenine

cytosine

guanine

thymine

yes

strands run in opposite directions (direction that C3 and C5 on sugar are facing)

covalent phosphodiester bond

break: polynucleotides break down
form: polynucleotides synthesised

adenine and guanine

thymine and cytosine

hydrogen bonds between nitrogenous bases

2

3

purine: 2 rings in base
pyrimidine: 1 ring in base

so equal-sized ‘rungs’ on DNA ladder which can then twist into double helix, providing stability

sugar-phosphate backbones of antiparallel polynucleotide strands

where phosphate group attached to C5

where phosphate group attached to C3

nucleus

1

large DNA molecule tightly wound around histone protein

as loops without histone proteins in mitochondria and chloroplasts

DNA loop in cytoplasm without histone protein (described as naked)

in naked loop (no histone protein)

enzyme that catalyses formation of DNA from activated deoxyribose nucleotides using single-stranded DNA as a template

enzyme that catalyses breaking of H bonds between nitrogenous pairs of bases in a DNA molecule

all DNA within cell

during interphase before cell divides

-unwind: double helix untwisted catalysed by gyrase enzyme
-unzips: H bonds between nucleotide bases are broken catalysed by DNA helicase resulting in 2 single strands of DNA with exposed bases

2 identical DNA molecules each containing 1 new strand and 1 old strand

different versions of a particular gene

gene variants

enzymes proofread and edit out incorrect nucleotides reducing rate mutations are made

a change with one nucleotide causing a change to genetic code

after unwinding and unzipping…
1) free phosphorylated nucleotides in nucleoplasm bond to exposed bases following base pairing rules
2) DNA polymerase enzyme catalyses addition of new nucleotide bases (in 5’ to 3’ direction) to single strands of DNA
3) leading strand synthesised continuously and lagging strand in fragments (discontinuous) that are later joined (catalysed by ligase enzymes)
4) hydrolysis of activated nucleotides (which release extra phosphate groups) supply energy to make phosphodiester bonds between sugar residue and phosphate group of different nucleotides

semi-conservatively, bubble sprouts from loop which unwinds and unzips and then complementary nucleotides join exposed nucleotides until whole loop copied

length of dna coding for a polypeptide or for length of RNA involved in regulating gene expression

process of making messenger RNA from DNA template

formation of a protein at ribosomes by assembling amino acids into particular sequence according to coded instructions carried by mRNA

ribose instead of deoxyribose

uracil (pyrimidine) replaces thymine

-single-stranded not double
-shorter

-messenger (mRNA)
-transfer (tRNA)
-ribosomal (rRNA)

sequence of DNA base triplets

so polypeptide can fold correctly and hold tertiary shape

shape of active site must be complementary to shape of substrate molecule

must be complementary to shape of antigens on invading pathogen

must be complementary to shape of cell signalling molecule (eg drug)

hydrophilic amino acids lining inside of channel
lipophilic amino acids on outside portion next to lipid bilayer

base triplet

codon

anticodon

copy of each gene transcribed into length of mRNA which passes through nucleus into cytoplasm and to ribosome

-universal
-degenerate
-non-overlapping

same triplet of bases codes for same amino acids in almost all organisms

for nearly all amino acids theres more than one base triplet

reduce effect of point mutations as change in one base can still code for same amino acid

read starting from a fixed point in groups of 3 bases

causes frame shift and due to genetic code being non-overlapping every base triplet and therefore amino acid is changed

-gene unwinds and unzips
-H bonds between complementary nucleotide bases break
-enzyme RNA polymerase catalyses formation of temporary H bonds between RNA nucleotides and complimentary unpaired DNA bases
-mRNA now passes out of nucleus through nuclear envelope and attaches to ribosome

strand that bonds with mRNA during transcription

what RNA is a copy of

-made in nucleolus in 2 smaller subunits which pass separately out of nucleus through pores in nuclear envelope
-magnesium ion helps bind 2 subunits together

ribosomal RNA and protein in roughly equal parts

nucleolus

-single stranded polynucleotides that twist into hairpin shape
-one end is trio of nucleotide bases which recognises and attaches to specific amino acid
-at loop end anticodon which is complementary to specific codon on mRNA

1) tRNA molecules bring amino acids and find place where anticodon binds by temporary H bonds to complimetary codon on mRNA
2) as ribosome moves along mRNA it reads code and when 2 amino acids are adjacent peptide bond forms between them
3) newly synthesised polypeptide helped by chaperone proteins to fold into correct tertiary structure

breaks down and components can be recycled into new lengths of mRNA

coding strand

template strand