Transcription Flashcards
DNA--> RNA
Central Dogma of molecular biology
The process by which instructions in DNA are converted into a functional product
DNA–> RNA–> Protein
DNA
Very stable Double helix Template 'Holy Grail' Around forever Deoxyribose
RNA
We can make it and break it down
We make lots of it
It degrades
Single stranded
Ribose
RNA is a linear polymer made of 4 different types of nucleotides
Can form a secondary structure
Commonly formed intra-molecular base pairs found within the same molecule.
Has a 3D structure structure determined by the nucleotide sequence – this enables RNA to also have structural and catalytic roles
What are the 4 ribonucleotides in RNA
Adenine
Guanin
Cytosine
Uracil –> this can base pair with Adenine
The complementary base pairing is the same as DNA
Transcriptions simple
Transcription involves partial DNA unwinding
One of the DNA strands acts as a template for RNA synthesis
The new RNA chain is called a transcript
Immediately after RNA synthesis the DNA rewinds displacing the RNA chain
Transcription is carried out by RNA polymerases
The start of each RNA can be made before the previous one has finished
RNA polymerase has no proof reading ability
–> Mistakes are made at 1 in 10^4 nucleotides
Because its dispensable this isn’t really a problem, the protein just won’t be used
What are the three types of RNA
mRNA - Messenger- Codes for proteins
rRNA - Ribosomal- forms the core of the ribosome
tRNA- Transfer - Selects the amino acids for the ribosome
One mRNA carries the information for one gene which codes one protein
Forming mRNA
The DNA is pulled apart
The DNA polymerase replicates the new strand –> then works through the replication origins
The two strands are pulled apart by an RNA polymerase–> this is a different enzyme with a similar function
The RNA polymerase slides along the DNA. As it does so we take some individual nucleotides (some RNA substrates) and they base pair with one of the single stands.
This forms a new stand of RNA transcript
There is directionality
How do we turn genes on and off
This is controlled by transcription
RNA polymerase weakly attaches to DNA and slides along it
It then meets a promotor (start site) - Once it recognises a promotor it is committed
The DNA chain is then opened and RNA synthesis occurs on one strand.
This continues until RNA polymerase reaches a terminator ( stop site)- This is a particular amino acid –> Blank –> allows the message to drop off
Polymerase halts and releases DNA and RNA
DNA double stranded nature means what
You can have coding genes on either strand. The directions in which they lie is anti parallel
What are the main differences seen between Eucaryotic and Procaryotic Cells
In Eucaryotes
- RNA capping is at the 5’ end and usually involves a guanine with a methyl group (cap)
- Polyadenylation is at the 3’ end
(tail) - These increase stability. The RNAzes that breakdown RNA tend to start at one end and breakdown. If the head and tail are present, the slows/prevents degredation
- Nuclear RNA is identified by a G cap and a poly A tail
- As RNA stays in the nucleus it gets shorter
- It was found that they have
- -> Introns: non coding DNA
- -> Exons : Coding DNA
Exons are usually shorter than introns and the coding part of the gene is often a small section of the total DNA
Introns are removed by RNA splicing in the nucleus to form mRNA . Then removed by small nuclear ribonucleoprotein particle
RNA has to be exported through nuclear pores
RNA undergoes processing from the primary transcript
Are promotor sequences symetrical
No they are asymmetrical
Only one DNA strand is actually converted to RNA
Snurps and Lariats
Lariats - loops
Snurps -Small nucleo ribio nucleotide particle
Stitch the exons together whilst ‘looping’ out the introns leaving a protein
Help catalyse the exons attachment to each other
This shortens the length of the mRNA
How is the amount of protein in a cell determined
The amount of time the mRNA spends in the cel
mRNA molecules are degraded by the cell to the nucleus
The lifetime of the mRNA differs depending on its location
Stable mRNA codes for a highly expressed protein
Unstable mRNA codes for a low protein expression
Alternative splicing
Not every exon is used which means multiple proteins can be formed from the same RNA strand
The regulatory elements in the mRNA sequence decide which exons will be spliced out
This means similar but slightly different proteins are formed.
