6 - Nucleic acids and protein synthesis Flashcards
What is a gene?
A sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that in turn make up a specific polypeptide (protein)
(___) gene(s) code(s) for (___) mRNA molecule(s), which code(s) for (___) polypeptide(s)
One gene codes for one mRNA molecule, which codes for one polypeptide.
What is a codon?
A sequence of 3 bases (triplet) which codes for one amino acid
How many different amino acids do our cells use?
20
How many different triplet combinations are possible?
64
Do the same codons code for the same amino acids in all living things?
Yes.
What stages make up protein synthesis?
1 - transcription - DNA is transcribed → mRNA molecule produced.
2 - translation - mRNA is translated → amino acid sequence is produced.
Where in the cell does transcription occur?
Nucleus
What steps occur in transcription?
1 - part of a DNA molecule unwinds (H-bonds between base pairs break) → exposes gene to be transcribed
2 - complementary copy of code from gene is made (single-stranded mRNA molecule)
3 -
PMT
Name the pentose sugars in DNA and RNA
Deoxyribose in DNA
Ribose in RNA
Describe the structure of DNA
Double-stranded polymer of nucleotides twisted to form a double helix.
Nucleotides joined by phosphodiester bonds.
Hydrogen bonds form between complementary base pairs (A+T, C+G).
Antiparallel strands.
What are the two groups of nucleotide bases?
Purine
Pyrimidine
Name the purine bases and describe their structure
Two-ring molecules:
Adenine - C₅H₅N₅
Guanine - C₅H₅N₅O
Name the pyrimidine bases and describe their structure
One-ring molecules:
Thymine - C₅H₆N₂O₂
Cytosine - C₄H₅N₃O
Uracil - C₄H₄N₂O₂
What is complementary base pairing?
Describes how H-bonds form between complementary purine and pyrimidine bases.
2 bonds between A+T (or A+U)
3 bonds between G+C
Why is DNA replication described as semiconservative?
Strands from original DNA molecule act as templates.
New DNA molecule contains 1 old strand and 1 new strand
How is a new strand formed during semiconservative replication?
1 - Free nucleotides from nuclear sap attach to exposed bases via complementary base pairing
2 - DNA polymerase joins adjacent nucleotides on new strand in a 5’ → 3’ direction via condensation reactions to form phosphodiester bonds.
3 - Hydrogen bonds form between complementary base pairs.
Outline the role of DNA ligase in DNA replication
ChatGPT
What components make up a nucleotide?
A phosphate group, a sugar and a nitrogenous base.
What is the structure of adenosine triphosphate (ATP)?
ATP is a phosphorylated nucleotide with three phosphate groups
Differentiate between purines and pyrimidines, and provide examples of each.
Purines:
Adenine and Guanine
Characterised by: double-ring structure.
Pyrimidines:
Cytosine, Thymine (DNA) and uracil (RNA)
Characterised by: single-ring structure.
