2.1.3 Nucleic acids and Nucleotides Flashcards
What does a nucleotide comprise of
- pentose sugar
- nitrogenous base
- phosphate group
What are the components of DNA nucleotide
- deoxyribose sugar
- Adenine, Cytosine, Guanine and Thymine
- phosphate group
What are the components of an RNA nucleotide
- ribose sugar
- Adenine, Cytosine, Guanine and Uracil
- phosphate group
Which bases are purines
Adenine and Guanine
What is the structure of purines
double ring structure
Which bases are pyrimidines
Cytosine, Thymine and Uracil
What is the structure of pyrimidines
single ring structure
What is the difference in structure between a deoxyribose and ribose sugar
in deoxyribose, carbon 2 has an OH group whereas the carbon 2 on ribose has an H group
What reaction joins nucleotides together
condensation reactions between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide
What bond is formed between nucleotides
a phosphodiester bond
- consists of a phosphate group and two esters
How are the strands of nucleotides arranged
antiparallel as they run in opposite directions
one strand is the 5’ to 3’ strand and the other is the 3’ to 5’ strand
Which carbons in the pentose sugars do the phosphate groups bond to during a condensation reaction
phosphodiester bonds link the 5-carbon of one deoxyribose sugar to the phosphate group from the same nucleotide
this phosphate group is joined to the 3-carbon of the deoxyribose sugar on the next nucleotide
What type of bonds hold nitrogenous bases together
hydrogen bonds
How many bonds form between Adenine and Thymine
2 hydrogen bonds
How many bonds form between Guanine and Cytosine
3 hydrogen bonds
What is the name of the process in which DNA is copied
semi-conservative replication
Describe the process of semi-conservative replication
DNA helicase breaks the hydrogen bonds between the base pairs
free DNA nucleotides are brought to exposed bases on each of the template strands
adjacent nucleotides are joined by DNA polymerase to form new sugar phosphate backbone with phosphodiester bonds
hydrogen bonds form between complementary bases
What is the function of DNA polymerase
catalyses the formation of phosphodiester bonds between adjacent nucleotides
Why is it important to conserve one DNA strand
- maximises accuracy as each new DNA strand is created from an existing template
- ensures genetic continuity between generations of cells (as cells will contain the same genetic information as their parent cells)
What is a potential consequence of semi conservative replication
can lead to random, spontaneous mutations (changes to the base sequence)
- extra base inserted
- bases inserted in the wrong order
- a base being left out
What is a gene
a sequence of nucleotides that codes for the production of a specific protein
How many bases code for one amino acid
three
known as a codon/triplet
Give three features of the genetic code
- non-overlapping
- degenerate
- universal
Why is the genetic code said to be degenerate
multiple codons can code for the same amino acid
- this can limit the effect of mutations
Why is the genetic code said to be non-overlapping
each base is only read once in which codon it is a part of
Why is the genetic code said to be universal
almost every organism uses the same code (a few exceptions)
- the same triplet codes for the same amino acids in all species (useful for genetic engineering)
What is an anticodon
part of a tRNA molecule which is complementary to the codons on mRNA
Describe the process of transcription
helicase breaks the hydrogen bonds between complementary base pairs
free RNA nucleotides pair up with their complementary bases on the template strand of the exposed DNA
RNA polymerase catalyses the reaction between nucleotides to form a sugar-phosphate backbone
the mRNA molecule leaves the nucleus via the nuclear pore
Describe the process of translation
the first triplet is read by the ribosome
tRNA has an anti-codon which is complementary to the specific codon on mRNA
this allows the tRNA to bring the correct amino acid to the ribosome
- process continues with next triplet being read
amino acids are joined with peptide bonds
continues until a stop codon is read
