L2 - Structure and Properties of RNA Flashcards
Describe the relationship between DNA, genes and the genome
The DNA encodes gene and the genes are the protein coding regions of the genome
What role do ‘junk’ genes hold?
- Not directly involved as genes in protein coding but act as regulators for the expression of those genes
- Important for stability and expression, as well as regulation of individual regions on individual chromosomes
What is a gene coding for?
A protein
What intermediate is used to express genetic information from genes to form a protein?
RNA
What slight structural difference is there between DNA and RNA? Why does this make a difference
- 2-deoxyribose has a hydrogen on the 2’ carbon
- Ribose has a hydroxyl group on the 2’ carbon
Why does the hydroxyl group on the 2’ carbon in ribose in RNA affect its stability?
Makes RNA more prone to degradation because the phosphodiester bond formed between subsequent nucleotides is less stable than it is in DNA
What nitrogenous bases are in RNA?
Adenine
Guanine
Cytosine
Uracil (no thymine)
How does uracil differ to thymine? Why does this make a difference?
Uracil has a hydrogen
Thymine has a methyl group
Uracil is demethylated so is less stable
What is thymine more resistant to than uracil? How does this make a difference?
- More resistant to photochemical mutation
- Enables DNA to be more resistant to mutagens, maintaining the fidelity of DNA
- RNA is therefore more prone to degradation
What direction is RNA read in?
5’ to 3’ direction
What are the main properties of RNA?
- RNA is single stranded
- RNA had uracil instead of thymine
- RNA has ribose not 2-deoxyribose
- Sequence comes from DNA
- RNA carries genetic information
- Shorter than DNA
- Can form hairpin structures
What is the main functional difference between a gene and RNA?
A gene codes
RNA expresses the protein
Describe the structure of a single strand of RNA
- Starts at the 5’ end and moves into the stem
- Loops into a hairpin
- Back along the stem to the 3’ end
- The stem has complementary base pairing between bases to aid stability and allow the RNA to remain in the nucleus for long enough - less vulnerable to degradation
How many loops does tRNA have?
- 3 conserved loops
- 1 small variable loop - dependent on the type of tRNA
What do all tRNA molecules have in common?
An acceptor stem which has the amino acid that is being coded for by the anticodon, which is read from the RNA
How many domains does mRNA have? What do the domain sizes depend on?
- 4 domains (still single stranded)
- Size is dependent on the length of the transcript that has come form the gene
Define transcription
The synthesis of RNA under the direction of DNA - uses DNA as a tmeplate
Define translation
The actual synthesis of a protein, which occurs under the direction of mRNA
What determines all visible phenotypes?
Result of actions of enzymes, which are proteins that catalyse and regulate all bodily functions
What would a change that affects proteins effect?
Would potentially affect the expression of phenotypes
Give an overview of the process of transcription
1) The DNA double helix is opened up by helicase, to allow access for transcriptional machinery to the coding region
2) 2 SSBP keep the conformation open
3) RNA polymerase reads the code to make complementary mRNA using the other strand in the 3’-5’ direction as a template
4) pre-mRNA is formed first, which forms a transcript of the whole of the coding region from a gene through translation
5) RNA processing happens which forms mature mRNA from pre-mRNA by removing introns, and splicing together exons.
6) Mature mRNA is transported out of the nucleus via nuclear pores into the cytoplasm to the ribosomes on the RER for translation. This produces a polypeptide chain
Where does transcription occur?
In the nucleus
Where else can the process of transcription and translation take place?
In a mitochondrion - mitochondrial DNA and expression remain with that mitochondrion