Nucleic Acids Flashcards
What bases are Purines?
Adenine and Guanine
What bases are Pyrimidines?
Thymine and Cytosine
What bases pair together, and how many hydrogen bonds form between these?
Adenine and Thymine = two H bonds
Cytosine and Guanine = three H bonds
What is the structure of ATP?
1 adenine group (nitrogenous base)
1 ribose sugar
3 inorganic phosphates
Function of ATP:
transfers energy
it is the universal energy molecule and an immediate source of energy the phosphate(s) can be removed by hydrolysis to release 30kJ (mol-1) energy
releases energy for metabolism such as muscle contraction, active transport, phosphorylation, glycolysis
during movement binding to proteins to change their shape
ADP can attach a phosphate (forming ATP) during respiration / photosynthesis
energy is released in small ‘packets’ (to prevent cell damage)
Structure of DNA
deoxyribonucleic acid (DNA) is a polynucleotide, usually double stranded, made up of nucleotides containing a nitrogenous base (adenine(A), thymine(T), cytosine(C) or guanine(G), the sugar deoxyribose and a phosphate group
Structure of RNA
ribonucleic acid (RNA) is a polynucleotide, usually single stranded, made up of nucleotides containing a nitrogenous base (adenine(A), uracil(U), cytosine(C) and guanine(G)), the sugar ribose and a phosphate group.
What are the 3 types of RNA?
mRNA - messenger
tRNA - transfer
rRNA - ribosomal.
What are the stages of DNA replication (semi conservative)?
The DNA is untwisted and unzipped by the enzyme helicase
This causes the H bonds between the complimentary bases to breaks
Both strands then act as template
Free DNA nucleotides complementary base pair C to G and T to A (purine to pyrimidine)
Hydrogen bonds reform
The sugar-phosphate back bone is joined by DNA polymerase forming phosphodiester bonds
What is a gene?
a sequence of DNA nucleotides that codes for a polypeptide;
Features of the genetic code?
It is a triplet code- three bases code of an amino acid
it is a degenerate code- All amino acids bar one have more than one code
Some codes don’t code for amino acids but are ‘stop’ codons- they indicate the end of the polypeptide chain
It is widespread but not universal- Codons generally always code for the same amino acid in every organism, but this is not always the case.
Stages of transcription:
1) RNA polymerase attaches to DNA double helix at beginning of gene
2) Hydrogen bonds between 2 dna strands break, uncoiling molecule
3) One strand is used as a template to make mRNA copy
4) RNA polymerase lines up free nucleotides alongside the template strand. Complementary base pairing means mRNA strand ends up being complementary copy of DNA template strand except T is replaced with U.
5) Once RNA nucleotides have paired up with specific bases on DNA strand, they join together forming mRNA molecule.
6) RNA polymerase moves along DNA separating strands and assembling mRNA strand.
7) Hydrogen bonds between the uncoiled strands of DNA reform once RNA polymerase has passed by and strands coil back into double helix.
8) When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from DNA.
9) The mRNA moves out of nucleus through a nuclear pore and attaches to ribosome in cytoplasm, where translation takes place.
Stages of translation:
1) mRNA molecule attaches to ribosome and tRNA molecule carries amino acids to ribosome.
2) tRNA molecule, with anticodon that’s complimentary to start codon on mRNA, attaches itself to mRNA via complementary base pairing.
3) A second tRNA molecule attaches itself to the next codon on mRNA in the same way.
4) rRNA in ribosome catalyses formation of peptide bond between 2 amino acids attached to tRNA molecules. This joins amino acids together. First tRNA molecule moves away, leaving amino acid behind.
5) A third tRNA molecule binds to next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away.
6) This process continues, producing a chain of linked amino acids (polypeptide chain), until there’s a stop codon on the mRNA molecule.
7) polypeptide chain moves away from ribosome, completing translation.
