DNA, RNA - transcription Flashcards
What is the central dogma?
DNA (replication in the nucleus) to RNA (transcription in the nucleus) to protein (translation in the cytoplasm)
DNA
- the genetic information in the nucleus
mRNA
- copies of genetic information travel from the nucleus to cytoplasm
protein
- made in the cytoplasm from genetic information carried by messenger RNA
What is gene expression?
process by which the information in genes
- is transferred to RNA and proteins
- give rise to effects on the cell = caused by proteins
- determines the appearance of the cell of the organism = phenotype (observable characteristics)
What are genes, DNA, proteins, ribonucleoproteins and genotype?
genes
- are made up of DNA = are short sections of DNA
DNA
- passive carrier of information
proteins and ribonucleoproteins
- carry out the function of the cell
ribonucleoprotein
- a complex of RNA and protein
genotype
- individuals collection of genes
What is the difference between intergenic regions, introns and axons?
intergenic regions
- are between genes = separates them
introns = also known as intervening sequences
- are a sequence within the genes = are non-coding
- are transcribed in RNA but are removed before RNA is exported to the cytoplasm
- can vary on size
exons
- are a sequence within the genes
- are transcribed as part of the primary transcript and are retained in the mature mRNA
What are untranslated regions (UTRs)?
untranslated regions = are exons
- a sequence within the mature mRNA
- are no translated = do not code for amino acids
- are non-coding regions
What are promoters?
promoter
- region of DNA that controls the binding of RNA polymers = initiates transcription
- is upstream of the start site
usually contains DNA sequence TATAA
- called the TATA box = about 30 base pairs
- TATA binding proteins bind to the TATA box and help the RNA polymerase to bind
region around the TATA box is called a basal promoter
- binds basal transcription factors
What are the differences between DNA and RNA?
DNA
- have deoxyribose sugar
- usually double stranded
- have nitrogenous bases = adenine (purine) with thymine (pyrimidine) and guanine (purine) with cytosine (pyrimidine)
- is more stable = more permanent store of genetic information
RNA
- have ribose sugar
- usually single stranded but can form a double helix only if the complementary strand is present
- have nitrogenous bases adenine (purine) with uracil (pyrimidine) and guanine (purine) with cytosine (pyrimidine)
- uracil can be used as mRNA is a temporary store of genetic information
- is less stable than DNA
Why can uracil be used in RNA not DNA?
uracil cannot be used in DNA because it easily/readily degrades to cytosine
- would result in the wrong codes as if it degrades it will match with guanine instead of adenine
makes it useful for temporary mRNA instead of permanent DNA
What are the similarities between DNA and RNA?
both have pentose sugars
- DNA has deoxyribose whereas RNA has ribose sugar
both have a phosphodiester bond between the 3 prime and 5 prime ends of adjacent pentose sugar molecules
- forms the sugar backbone of DNA double helix
both have a directionality of 5 prime to 3 prime
the nitrogenous bases (purines or pyrimidines) attached to 1’ carbon atom
What are the different types of RNA?
messenger RNAs (mRNA) - transmits the information from the genes to the ribosomes where it is translated into protein
transfer RNAs (tRNA) - ensure the correct amino acid matches the codon specified by the mRNA
ribosomal RNAs (rRNA) - form part of the ribosome structure
small nuclear RNA (snRNA)
- helps align sequences (introns) to be spliced (by spliceosomes) out of primary transcripts (immature mRNA)
How is RNA synthesised by RNA polymerase? What are NTPs?
NTPs
- ribonucleoside trisphosphates = nitrogenous base + pentose sugar + 3 phosphate molecules
RNA polymerase enzymes covalently link the free -OH group on the 3’ carbon of a growing chain of nucleotides to the alpha-phosphate on the 5’ carbon of the next (d)NTP
this releases the β- (beta) and γ- (gamma) phosphate groups as pyrophosphate (PPi)
results in a phosphodiester linkage between the two (d)NTPs
the release of PPi provides the energy necessary for the reaction to occur
occurs exclusively from 5 prime to 3 prime direction
What are the three types of RNA polymerase in eukaryotes and their function?
RNA polymerase I - transcribes rRNA genes
RNA polymerase II - transcribes mRNA
RNA polymerase III - transcribes tRNA and other small RNAs
What is the function of a sigma factor?
is found in prokaryotes and are not in eukaryotes
sigma factor
- is a protein that enables the RNA polymerase to bind to the promoter and initiates transcription
- affects the binding affinity of RNA polymerase to promoters
What is the Rho protein? What is the function of the Rho protein?
Rho protein is a protein found in prokaryotes that terminates transcription
Rho independent
- no Rho protein
- RNA polymerase encounters the C-G stem loop (stabke secondary structure) which is followed by multiple uracil nucleotides
- the weak adenine-uracil bonds lower the energy of destabilization for the RNA-DNA duplex, allowing it to unwind and dissociate from the RNA polymerase
Rho dependent
- has Rho protein
- the rho-protein locates and binds the signal sequence in the mRNA and signals for cleavage when it moves along the sequence and comes into contact with the RNA polymerase
What processing does eukaryotic mRNA go under before it is translated?
capping
- a nucleotide is attached to the end of the strand
- the nucleotide added is opposite to the directionally of the strand = means 5 prime nucleotide is added to the 3 prime end and vice versa
- stops the RNA from being attacked by endonuclease (cleave the phosphodiester bond) before transcription is over and helps ribosome attach to mRNA
polyadenylation = poly A tail
- at termination of transcription, around 200 adenine are added to the 3 prime end = makes it more stable
- prevents degradation and helps protect mRNA in the export
splicing
- introns are removed by small rRNA = spliceosomes
