class notes 1 - DNA structure and function Flashcards
what does DNA stand for?
Deoxyribonucleic acid
what is the basic unit of a DNA molecule?
a nucleotide
what are the components of a nucleotide?
a phosphate group, a deoxyribose sugar and an organic base
what are some examples of organic bases?
adenine, guanine, cytosine or thymine (A,G,C,T)
what is the pattern for base pairing?
base pairing always occurs between purines and pyrimidines, e.g, A-T and G-C
what is the central dogma of DNA?
DNA –> mRNA –> Protein –> inherited traits
what is the modern definition for a gene?
a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions, and or other functional sequence regions.
or
DNA/RNA whose function ultimately determines or influences a trait.
what is transcription?
> occurs in the nucleus.
is the process of copying a gene
this copying process results in the formation of messenger RNA (mRNA)
What are the steps in transcription? (see diagram)
> RNA polymerase unwinds and opens the DNA Helix then attaches to the ‘template’ strand of the DNA molecule and begins transcribing
Laying down RNA nucleotides that base pair with the DNA nucleotides
The triplet code on the DNA codes for a specific amino acid.
What amino acid replaces T(Thymine) on the RNA?
U (uracil) hence A-U
What is a triplet code on the mRNA called?
a codon
What are the steps in translation? (see diagram)
1) mRNA leaves the nucleus (via a nuclear pore) and enters the cytoplasm
2) Ribosome(s) attach to the mRNA (at the ‘start; sequence) and begin translation. In the diagram, translation is from left to right. The ribosome aligns two tRNA molecules at any given time. Note that there is a base sequence (called an anti-codon) on the tRNA that is complementary to the codon sequence of the mRNA.
3) once a peptide bond is formed between the two amino acids, the ribosome moves along to the next codon sequence. Translation continues until a ‘stop’ sequence is reached.
What do all mRNA sequences start and end with?
> ‘start’ - AUG
> ‘stop’ - UAA, UAG or UGA
What is the genetic code for amino acids known as a ‘degenerate code’ ?
it Basically means that there is redundancy in the code. For instance, for some amino acids there are multiple codes (e.g., Leu has six codes and Val, Ser and Pro each have four codes)
