nucleic acids and DNA replication Flashcards
DNA replication
DNA helicase unwinds the double helix by breaking H-bonds
makes it single stranded - both used as template
DNA nucleotides form hydrogen bonds with complimentary bases on DNA strand
AT 2, GC 3
DNA polymerase forms phosphodiester bonds between new DNA nucleotides
nucleic acids
2 types - deoxyribonucleic acid and ribonucleic acid
elements - C, H, O, N, P
monomer - nucleotide
- phosphate group, pentose sugar, nitrogenous base
carry the genetic code for the production of proteins
- common to all living organisms and viruses providing evidence for evolution
nitrogenous bases
purines - 9 membered ring
A, G
pyrimidines - 6 membered ring
T, C, U
condensation of nucleotides
phosphodiester bond between the OH of C3 of the 1st nucleotide and phosphate group of the 2nd
- every polynucleotide chain has unbonded P at beginning (5 prime end) (5C)
- finished with unbonded OH - 3 prime end
polynucleotide chains
RNA - only one - single stranded
DNA - two - double stranded
double helix - 2 strands twist around eachother
- are anti-parallel
- held together by H-bonds between complimentary nucleotides
the molecule is more stable, ie if bases mutated/ damaged one strand - can be copied correctly from other strand
nucleotide bonding
A + T - 2 bonds
C + G - 3 bonds
similarities
P group
OH group
phosphodiester bonding
A, C, G
functions of DNA
- DNA Replication = passing on genetic information from one generation to the next.
- Protein Synthesis = DNA base sequence carries the code for the primary structure / aa sequence of proteins.
DNA - transcription - tRNA, mRNA, rRNA
- translation - polypeptide
functions of RNA
mRNA - messenger RNA - carries the code for the amino acid sequence from the DNA to the ribosome - complementary sequence to 1 gene from DNA with introns sliced out - codons can be translated into a polypeptide by ribosomes
rRNA - ribosomal RNA - component of a ribosome
tRNA - transfer RNA - carries a specific amino acid to mRNA codons during translation
ATP synthesis
by a kind of condensation reaction known as PHOSPHORYLATION (addiction of a P group)
ATP synthase
ATP hydrolase
endothermic reaction - occurs during anaerobic and aerobic respiration and photosynthesis
ATP
adenosine triphosphate - energy currency of the cell - energy storage
where does energy come from
energy to phosphorylate ADP comes from glucose in respiration and light in photosynthesis
functions of ATP
hydrolysis - 30-31Kj
- active transport
- muscle contraction
add to
3 possible replication models
conservative replication - original + new
semi conservative - each daughter DNA molecule has one old strand and one new strand
dispersive - each daughter DNA molecule has a random mixture of old and new
evidence of semi conservative bias
Semi-Conservative DNA Replication is defined as:
- both DNA strands are used as templates for replication.
- each new daughter DNA molecule has one old / original strand and one new strand.
- growth medium with 15 nitrogen - grown for many generations so all DNA contain 15 N
- growth medium with 14 N grown for one generation (repeated with other molecules so many different generations)
- from each flask, a few cells removed and DNA extracted from them - centrifuged
- first (15N) last (14N) middle (mixture)
spec notes on replication
The process of semi-conservative replication of DNA in terms of:
unwinding of the double helix
breakage of hydrogen bonds between complementary bases in the polynucleotide strands
the role of DNA helicase in unwinding DNA and breaking its hydrogen bonds
attraction of new DNA nucleotides to exposed bases on template strands and base pairing
the role of DNA polymerase in the condensation reaction that joins adjacent nucleotides.
function of semi conservative replication
ensures genetic continuity between generations of cells.
spec notes nucleotides
DNA holds genetic information
RNA transfers genetic information from DNA to the ribosomes
Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from a pentose, a nitrogen-containing organic base and a phosphate group
spec notes ATP
A single molecule of adenosine triphosphate (ATP) is a nucleotide derivative and is formed from a molecule of ribose, a molecule of adenine and three phosphate groups.
Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) is catalysed by the enzyme ATP hydrolase.
The hydrolysis of ATP can be coupled to energy-requiring reactions within cells.
The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive.
ATP is resynthesised by the condensation of ADP and Pi. This reaction is catalysed by the enzyme ATP synthase during photosynthesis, or during respiration.
role of DNA in living cells
base sequence of genes codes for functional RNA and amino acid sequence of polypeptides
genetic information determines inherited characteristics = influences structure and function of organisms
relate the structure of DNA to its functions
sugar-phosphate backbone and many H-bonds provide stability
long molecule stores lots of information
helix is compact for storage in nucleus
base sequence of triplets codes for amino acids
double-stranded for semi-conservative replication
complementary base pairings for accurate replication
weak H-bonds break so strands separate for replication
structure and function of mRNA
long ribose polynucleotide (shorter than DNA)
uracil instead of thymine
single stranded and linear
codon sequence is complementary to exons of 1 gene from 1 DNA strand
breaks down quickly so no excess polypeptide forms
ribosomes can move along strand and tRNA can bind to exposed bases
can be translated into a specific polypeptide by ribosomes
structure of tRNA
single strand of about 80 nucleotides
folded into clover shape (some base pairings)
anticodon on one end, amino acid binding site on other
anticodon binds to complimentary mRNA codon
amino acid corresponds to anticodon
role of ATP in cells
ATP hydrolase catalyses ATP -> ADP + Pi
energy released is coupled to metabolic reactions
phosphate group phosphorylates compounds to make them more reactive
why ATP is suitable as the energy currency
high energy bonds between phosphate groups
small amounts of energy released at a term = less energy wasted as heat
single-step hydrolysis = energy available quickly
readily resynthesised
