nucleic acids Flashcards
what are nucleotides?
the monomers from which nucleic acids, like DNA and RNA are formed
what are the 2 types of nitrogenous bases?
purines & pyrimidines
what are purines?
2 carbon ring structures (adenine & guanine)
what are pyrimidines?
1 carbon ring structure (cytosine, thymine & uracil)
what pentose sugar is in DNA?
deoxyribose
what pentose sugar is in RNA?
ribose
what are the 3 components of a nucleotide?
nitrogenous group, phosphate group & pentose sugar
what are the complimentary base pairs in DNA?
thymine & adenine
guanine & cytosine
what are the complimentary base pairs in RNA?
uracil & adenine
guanine & cytosine
why is it important that purine and pyrimidine bases are always complementary to each other?
to help maintain the order of the genetic code when DNA replicates
what reaction bonds nucleotides together?
condensation reaction
what bonds form between the nucleotide monomers?
phosphodiester bonds
when the nucleotide monomers bond together, what does this create, and what is it called?
a polymer called a polynucleotide
what type of bond is a phosphodiester bond?
a strong covalent bond
where does the phosphodiester bond form?
between the pentose sugar, and phosphate group of different nucleotides
what is the structure of ATP?
pentose sugar which is always ribose, nitrogenous base which is always adenine & three phosphate groups
what is the function of the phosphate groups in ATP
energy transfer
what is ATP used for?
- essential for metabolism
- immediate source of energy for biological processes
where is ATP made?
during respiration (mostly aerobic) via a condensation reaction, using the enzyme ATP synthase
what enzyme hydrolyses ATP?
ATP hydrolase
what happens when ATP is hydrolysed?
- a small amount of energy is released
- the inorganic phosphate group that has been released, can be bonded onto a different compound, which makes the compound it’s bonded to more reactive, this is called phosphorylation
what does DNA code for?
the sequence of amino acids in the primary structure of a protein
what does the primary structure of a protein determine?
the final 3D structure & function of a protein
what is the structure of DNA?
the polymers form a double helix made of 2 antiparallel strands, which are joined together by hydrogen bonds between the bases on the 2 different strands
why does DNA have a stable structure?
due to the sugar-phosphate backbone with covalent bonds, and the double helix structure
why is DNA double-stranded?
so that replication can occur using both strands as a template
why are there weak hydrogen bonds between the complimentary bases?
it benefits DNA replication, because there is very little energy required to break the bonds & separate the 2 strands to use them both as a template
why is DNA a large molecule?
so that it can carry lots of information
why are there complimentary base pairs in DNA?
it allows identical copies to be made when DNA is replicated
what are the 3 types of RNA?
mRNA (messenger), tRNA (transfer) & rRNA (ribosomal)
what is the purpose of rRNA?
1 of the 2 components of ribosomes
what is mRNA?
a copy of one gene from DNA
what is the purpose of mRNA?
after it is created in the nucleus, it leaves via the nuclear pore to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm (protein synthesis)
why can mRNA leave the nucleus via the nuclear pore?
because it is much smaller than DNA
why is mRNA much shorter than DNA?
because it is only a copy of one gene
why is mRNA short-lived?
when it leaves the nucleus, and goes into the cytoplasm, it can become hydrolysed by enzymes in the cytoplasm
why does DNA not leave the nucleus?
the genetic code would be at risk of being hydrolysed by the enzymes in the cytoplasm
what is the structure of mRNA?
it is single-stranded
what are codons?
they are a ‘set’ of 3 bases in mRNA
what is the purpose of codons?
they code for one specific amino acid
where is tRNA found?
in the cytoplasm
what is the structure of tRNA?
single-stranded, but folded to create a cloverleaf shape, it is held in place by hydrogen bonds
what is the function of tRNA?
to bring specific amino acid to the ribosome
how is the structure of tRNA adapted to its function?
it has a specific shaped binding site which is determined by the 3 bases found on the tRNA (anticodon), this is complimentary to the 3 bases on mRNA (codon)
why is DNA replication described as semi-conservative?
because in replication one strand is conserved, and one new strand is created
what is a mutation?
when copying errors in DNA replication occur
when does DNA replication occur?
during S-phase in interphase of the cell cycle
why does the enzyme that catalyses DNA replication only attach to the 3’ end of the DNA?
it has a complimentary shape to only the 3’ end, not the 5’ end
what are the 4 stages of DNA replication?
- DNA helicase breaks down the hydrogen bonds between the complementary bases of the 2 DNA polymers, this causes the double helix to unwind and the 2 strands to separate
- these 2 strands then act as templates for DNA replication
- free-floating DNA nucleotides (which come from the nucleus) align opposite their complimentary base on the template strand of DNA. Hydrogen bonds then form between the base pairs of the new strand and the old strand
- DNA polymerase joins the adjacent DNA nucleotides together, which forms a phosphodiester bond between these nucleotides to create a new polymer chain of DNA
what are the 3 features of the genetic code?
degenerate, universal & non-overlapping
what does it mean that the genetic code is degenerate?
amino acids are coded for by more than one triplet of bases
what does it mean that the genetic code is universal?
the same triplet of bases codes for the same amino acid in all organisms
what does it mean that the genetic code is non-overlapping?
each base is only part of one triplet of bases that codes for one amino acid, each codon or triplet bases is read as a discrete unit
what is an advantage of the genetic code being degenerate?
even if a gene mutation occurs, which changes one of the bases in a triplet, it might mean that it still codes for the same amino acid, and the mutation therefore has no impact on the final sequence of amino acids in the polypeptide chain, and therefore the protein’s shape & function
what is an advantage of the genetic code being universal?
the same triplet of bases codes for the same amino acid in all organisms
what is an advantage of the genetic code being non-overlapping?
each base is only part of one triplet of bases that codes for one amino acid, each codon, or triplet of bases, is read as a discrete unit, this means that if there was a mutation, this would only effect one codon which would reduce the overall impact
what are the 2 stages of protein synthesis?
transcription & translation
what is transcription?
where the DNA sequence for one gene is copied into mRNA
what is translation?
where the mRNA joins with a ribosome (made of protein and rRNA), and a corresponding tRNA molecule brings the specific amino acid the codon codes for
what are introns?
sequences of bases in a gene that do not code for amino acids, they get removed (spliced) out of mRNA molecules after transcription
what are exons?
sequences of bases in a gene that code for a sequence of amino acids
what is the process of transcription?
- DNA helicase breaks the hydrogen bonds between the bases in the 2 strands of DNA
- this causes the DNA helix to unwind and one strand acts as a template
- free mRNA nucleotides align opposite exposed complimentary DNA bases
- the enzyme RNA polymerase joins together the adjacent RNA nucleotides, forming phosphodiester bonds, to create a new mRNA polymer chain
- once one gene is copied, the mRNA is modified and then leaves the nucleus through the nuclear envelope pores
what is the process of translation?
- once the modified mRNA has left the nucleus, it attaches to the small subunit of the ribosome at the start codon
- the tRNA molecule with the complimentary anticodon to the start codon aligns opposite the mRNA which is held in place by the ribosome, the ribosome can hold 2 tRNA molecules at a time
- the 2 amino acids that have been delivered by the tRNA molecule are joined together via a peptide bond which is catalysed by an enzyme using ATP
- the ribosome will move along the mRNA molecule to the next codon and another complimentary tRNA will attach to the next codon on the mRNA
- this continues until the ribosome reaches the stop codon at the end of the mRNA molecule causing the ribosome to detach and ends translation
- the polypeptide chain is now created and will enter the golgi for folding and modification
