Nucleic acids - structure and function Flashcards
Molecular Biology 2
Where is DNA mainly found?
In the cells nucleus
What does the backbone of DNA consist of?
Deoxyribose’s
How is the double-stranded DNA structure held together?
By hydrogen bonding
What shape does two chains of DNA wrapped round each other make?
Regular double helix structure (spiral)
What base does Guanine always pair with in DNA?
Cytosine
What does Adenine always pair with in DNA?
Thymine
What is the general structure of RNA?
- same 5’-3’ backbone as DNA
Where is RNA mainly found?
In the cytoplasm
How does RDA differ from DNA?
- Uracil replaced Thymine as a base
- Ribose replaces deoxyribose
- Single-stranded (no base pairings)
What is a ‘hairpin loop’?
Local double strand formation occurring in a single strand of RNA
What are the 3 types of RNA?
- Messenger RNA (5%)
- Transfer RNA (15%)
- Ribosomal RNA (80%)
What does the base sequence of DNA contain in all cells?
The genetic code
What are genes?
Specific stretches of DNA which code for a protein
What is the AA sequence of each protein determined by?
Nucleotide sequence of its corresponding gene
What is the whole genetic information within a single cell nucleus called?
The genome
What is involved in the process of transcription and translation?
- In the nucleus DNA unfolds to expose base pairs of template strand
- Transcription: RNA polymerase copies sequence of bases in template strand of DNA to produce mRNA
- mRNA translated by tRNA, using ribosome as a functional support in the cytoplasm
What is a codon?
Sequence of 3 bases in mRNA
What are ribosomes?
Small and large subunits, contain proteins and rRNA - act as a functional support and process of translation
What is tRNA’s role in translation?
- Carries each amino acid to ribosome (one specific tRNA for each amino acid)
- Contains anticodon (3 bases) complimentary to sequence of 3 bases (codon) on mRNA
- AA transferred to growing polypeptide chain
- Sequence of mRNA codons determines sequence of AA in a protein
How many possible codons are there?
64 possible codons
How many amino acids exist?
20 possible amino acids
What is meant by the genetic code being ‘degenerate’?
Some amino acids have more than 1 tRNA and hence more than one coding triplet - can be coded for by more than 1 codon
How do many degenerate codons differ?
Many codons specifying the same AA are grouped together, differing only in the 3rd base position e.g. Phe = UUU and UUC
What AA is known as the ‘universal start codon’?
Met
