Nucleotides and DNA - 2 Flashcards
What are nucleotides
Monomers of nucleic acids
What makes up a nucleotide
Contains a:
- Nitrogenous base
- Phosphate group
- Pentose sugar
What bond forms between nucleotides
A phosphodiester bond
What are the 5 nitrogenous bases
Adenine
guanine
Thymine
Cytosine
Uracil
What is the difference between a purine and a pyrimidine
Purines have a double ring structure whilst pyrimidines have a single ringed structure
Which bases are purines
Adenine
Guanine
Which bases are pyrimidines
Thymine
Cytosine
Uracil
How many hydrogen bonds do A and T make
Two hydrogen bonds
How many hydrogen bonds do C and G make
Three hydrogen bonds
What does anti-parallel mean
The 2nd strand must be upside down in order for base pairs to join
Explain how DNA is replicated
1) The double helix is untwisted by the enzyme gyrase
2) the hydrogen bonds are broken down by helicase
3) Each strand acts as a template
4) Free DNA nucleotides in the nucleus start to align with exposed nucleotides
5) Complementary base pairing occurs
6) Hydrogen bonds reform
7) Phosphodiester bonds are formed between the phosphate of one nucleotide and the sugar of another using the DNA polymerase
8) This creates two identical strands with half the original DNA
Describe three differences between RNA and DNA
RNA’s sugar molecule is ribose whereas DNA has deoxyribose
RNA has uracil instead of thymine
RNA nucleotide is single stranded where as DNA is double stranded
What is messenger RNA
A copy of the template strand of DNA
Has codons
Involved in transcription and translation
What is Ribosomal RNA
Complex molecule and accounts for half the mass of a ribosome
What is transfer RNA
Small, single stranded
Clover leaf shape
Has binding site for specific amino acids
Has an anticodon
Describe transcription
1) Gene to be transcribed unwinds and helicase breaks the hydrogen bonds
2) RNA nucleotides bind to complementary bases on the template strand
3) RNA polymerase catalyses formation of phosphodiester bond between RNA nucleotides
4) mRNA is complementary to the template strand and a copy of the coding strand
5) mRNA released from DNA , leaves nucleus, through nuclear pore to ribosome
Describe Translation
6) mRNA binds to a ribosome
7) tRNA attaches and its anticodon binds to the first codon
8) Second tRNA binds to the exposed codon via its anticodon
9) Peptide bonds form between the 2 amino acids
10) Ribosomes moves along the mRNA
11) A 3rd tRNA brings another amino acid
12) 1st tRNA leaves and is able to collect another amino acid
13)The polypeptide chain grows until a stop codon is reached
14) There are no corresponding tRNA’s so translation stops
What does universal mean
All living organisms use the same code
What does degenerate mean
for most amino acids there is more than one
base triplet
What does non-overlapping mean
it is read starting from a fixed point in
groups of three
