2.3 Nucleic Acids Flashcards
What is the structure of a purine base?
2 carbon-nitrogen rings
What is the structure of a pyrimidine base?
1 carbon-nitrogen ring
How many hydrogen bonds form between Adenine and Thymine
2
How many hydrogen bonds form between Cytosine and Guanine
3
What is the difference between a DNA and RNA nucleotide?
DNA- Deoxyribose pentose sugar and A,T,C,G
RNA- Ribose pentose sugar and A,U,C,G (Uracil)
1 DNA molecule consists of _ anti-parallel polynucleotide strand(s).
2
What bond is formed/broken when polynucleotides are made or broken?
Phosphodiester
What gives DNA molecules stability?
The double helix created by hydrogen bonds and the sugar-phosphate backbone
What is the structure of ATP and ADP?
Ribose pentose sugar, nitrogenous base adenine and 2/3 phosphate groups
Why is it important that the DNA molecule is stable?
To protect the coded genetic information and base sequence
What are the complementary base pairs?
A-T and C-G
How is DNA organised in Eukaryotes?
Each DNA molecule is wrapped around a histone protein into a chromosome.
A loop of DNA inside mitochondria and chloroplasts
How is DNA organised in Prokaryotes
In a loop of ‘naked’ DNA
How can you purify and extract DNA?
Precipitation
What is precipitation?
Macerate the tissue, add a strong detergent then add ethanol so the DNA precipitates out of solution
What does DNA polymerase do?
An enzyme that catalyses the addition of new nucleotide bases, in the 5’ to 3’ direction to the single unzipped DNA strand
What does DNA helicase do?
An enzyme that catalyses breaking the hydrogen bonds between DNA polynucleotide strands
What is semi-conservative replication?
How DNA replicates, making 2 new molecules, each containing 1 old strand and 1 new strand- 1 old strand is conserved in each molecule
What is a genome?
All the DNA within a cell
What is the 1st thing a DNA molecule must do before it can replicate?
Unwind the double helix, catalysed by DNA gyrase and unzip, catalysed by DNA helicase
How is the leading strand synthesised?
Continuously
How is the lagging strand synthesised?
In Okazaki fragments discontinuously, that are later joined by DNA ligase
What are different versions of the same gene called?
Alleles
What is a gene?
A section of DNA that codes for a particular protein
What is a base triplet (codon)?
3 DNA bases which code for an amino acid
How is the genetic code non-overlapping?
It is read from start to finish in triplets, and each triplet is read separate from the ones before and after
How is the genetic code degenerate?
There are more than 1 base triplet for each amino acid, reducing effect of point mutation
How is the genetic code universal?
Because in all organisms the same triplet codes for the same amino acid
How does a gene determine the protein structure?
The order of nucleotide bases in a gene determines the order of amino acids in a protein (primary structure)
What are the roles of RNA polymerase in protein synthesis?
- It’s an enzyme that attaches to DNA at the beginning of a gene to begin transcription
- It catalyses formation of temporary hydrogen bonds between RNA nucleotides and the unpaired DNA bases.
What is messenger RNA (mRNA) for?
It carries the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm.
What is transfer RNA (tRNA) for?
To carry amino acids that are used in protein synthesis to ribosomes during translation
What is the structure of transfer RNA (tRNA)?
It has an amino acid binding site at one end and an anticodon (sequence of 3 bases) on the other end
Where is tRNA found?
Cytoplasm
What does ribosomal RNA (rRNA) do?
- It forms the 2 subunits of a ribosome alongside proteins
- rRNA catalyses formation of peptide bonds
What is transcription for?
To make an mRNA copy of a gene in the nucleus
What is translation for?
Amino acids are joined together to make a polypeptide following the mRNA codon sequence
During transcription, one DNA strand acts as a _______ to make an mRNA copy.
Template
What does RNA polymerase do in transcription?
Lines up free RNA nucleotides alongside the template strand, making the mRNA strand a complementary copy of the DNA template strand, and catalysing temporary hydrogen bonds between RNA nucleotides and DNA bases
What happens in translation?
mRNA attaches to a ribosome, and a tRNA that’s complementary to the starting codon attaches to mRNA by complimentary base pairing, until many tRNA’s have joined similarly and rRNA catalyses formation of pepide bonds between the amino acids, and the tRNA moves away leaving a polypeptide chain
