Nucleotides and nucleic acids Flashcards
Explain the structure of a nucleotide
a pentose sugar (ribose or deoxyribose), a phosphate group and a nitrogenous base
Name the pentose sugars in DNA and RNA
DNA: deoxyribose
RNA: ribose
Describe how polynucleotide strands form
Condensation reactions between nucleotides form strong phoshpodiester bonds
Describe the structure of DNA
Double helix of 2 deoxyribose polynucleotide strands, H bonds between complementary base pairs on opposite strands (AT&GC)
Describe the structure of RNA
Single stranded. Made up of ribose mononucleotides, linked through condensation reactions
Name the complementary base pairs in DNA
2 H bonds between Adenine and Thymine, 3 H bonds between Cytosine and Guanine
Name the complementary base pairs in RNA
2 H bonds between Adenine and Uracil, 3 H bonds between Guanine and Cytosine
Why is DNA replication described as semiconservative?
Strands of original DNA molecule act as templates, new DNA molecule contains one old strand and one new strand
Summarise the process of DNA replication
- Double helix unwinds and the hydrogen bonds break, catalysed by DNA helicase
- Complementary base pairing occurs
- The nucleotides are joined by phosphodiester bonds, catalysed by DNA polymerase
What is the role of the enzyme DNA polymerase in DNA replication?
It catalyses the formation of phosphodiester bonds between the free nucleotides to form the new complementary strand of DNA
Describe the Meselson and Stahl experiment procedure
- E. coli bacteria was grown in a growth medium containing an
isotope of nitrogen (15N) - The bacteria incorporated the isotope into the nucleotides
- The bacteria were allowed to divide and samples were taken
after each division - The samples were centrifuged using a salt with a density
gradient
What is the genetic code?
A term used to describe the linear sequence of nucleotides that determine the amino acid sequence in a protein
What is meant by a triplet code?
A section of DNA where groups of 3 nucleotides code for one amino acid
What is meant by the genetic code being non-overlapping?
The genes are read in order so that the order of the genes determines the order of the amino acids in the polypeptide
What is meant by the genetic code being degenerate?
Amino acids can be coded for by multiple different triplets. For example, AGA and CGA both code for the amino acid arginine
What is a gene?
A section of the DNA that codes for the sequence of amino acids in a protein
Describe the structure of messenger RNA
Long ribose polynucleotide with sugar-phosphate backbone. Nitrogenous bases A, U, G, C,. Single stranded and linear. Codon sequence is complementary to exons of 1 gene from 1 DNA strand
State the function of mRNA
Transfers genetic code from DNA in nucleus to ribosomes for translation into a specific polypeptide
What is the role of RNA polymerase in transcription?
It catalyses the formation of phosphodiester bonds between adjacent RNA nucleotides to form the mRNA strand
Outline the process of transcription
RNA polymerase binds to promoter region on a gene. Section of DNA uncoils into 2 strands with exposed bases. Antisense strand acts as template. Free nucleotides are attracted to their complementary bases. RNA polymerase joins adjacent nucleotides to form phosphodiester bonds
Describe the structure of transfer RNA
Single strand folded into clover shape. Anticodon on one end, amino acid binding site on the other
State the function of tRNA
Carries amino acids to specific codons on mRNA for translation
What is a codon?
Three consecutive nucleotides which code for one amino acid
What is an anticodon?
A sequence of three bases on a tRNA molecule which is complementary to a codon on an mRNA molecule
What does translation produce and where does it occur?
It produces proteins. It occurs in the cytoplasm on ribosomes
Outline the process of translation
1) mRNA travels to a ribosome
2) The mRNA is passed through the ribosome 3 bases (one codon) at a time
3) tRNA molecules with complementary anticodons to the mRNA codons
hydrogen bond
4) The ribosome catalyses the formation of peptide bonds between the
amino acids on the tRNA molecules
5) tRNA molecules leave, the ribosome moves along the mRNA and the
cycle repeats until the polypeptide has been synthesised
● This process requires ATP
What is a mutation?
A random change to the base sequence in DNA which results in genetic variants
List 3 types of mutations
Insertion, deletion, substitution
What is a substitution mutation?
Where one base gets swapped for another base
What is a deletion mutation?
Where one or more bases are removed. This results in a frameshift mutation which alters all the codons after the error
What is an insertion mutation?
Where one or more bases are added. This results in a frameshift mutation which alters all the codons after the error
Give 3 effects of mutations
They aren’t all bad
Harmful, neutral, beneficial
What is cancer?
A non-communicable disease which is characterised by uncontrolled cell division. It can be caused by mutations in regulatory genes.
