Genetics 1 Flashcards
What is the structure of a nucleotide?
Nitrogenous base, pentose sugar (deoxy/ribose), phosphate group(s).
Which nucleotides are purines and which are pyrimidines?
Pyramidines = cytosine, thymine, uracil
Purines = adenine, guanine
What are the differences between structure of DNA and RNA?
DNA = double-stranded, deoxyribose sugar, thymine base.
RNA = single-stranded, ribose sugar, uracil base.
Which bases pair in DNA?
A-T with two H bonds.
G-C with three H bonds.
Define ‘degenerate’.
Some amino acids are encoded by more than one codon (three bases).
What does mitochondrial DNA (mtDNA) encode?
Small number of mitochondrial proteins - always maternally inherited.
How are chromosomes formed from DNA?
DNA strands wrap around histones to form nucleosomes.
Multiple nucleosomes form chromatin.
Chromatin loops and condenses to form chromosomes.
What is a karyotype?
A picture of an individual’s chromosomes.
Describe the process of DNA replication.
Topoisomerase unwinds and helicase unzips double helix.
DNA polymerase copies leading strand, adding bases 5’->3’.
Lagging strand copied in short 5’->3’ sections called Okazaki fragments.
Ends when replication bubbles meet.
Describe the process of transcription.
Promoter sequences direct RNA polymerase to bind to DNA.
One DNA strand acts as template strand, other strand is called the coding strand.
RNA synthesised in 5’->3’ direction until termination sequence reached.
How are introns removed from pre-RNA?
Guanosine 5’ cap added to protect from degradation.
A poly A tail added at 3’ end to protect from degradation.
Introns removed and exons joined by splicing.
Describe the process of translation.
Ribosomes read mRNA in 5’->3’ direction in codons.
tRNA molecules match amino acids to codons on mRNA.
Ribosome detaches at stop codon, leaving strand of amino acids (primary protein).
