1.12. Expression of genes - transcription Flashcards
polygenic vs monogenic inheritance
monogenic - the trait results from the expression of only one gene (or one gene pair)
polygenic - results from the expression of multiple genes
gene
a part of DNA with a specific base-sequences that code for the a-a sequence of one polypeptide chain
gene expression
transcription of a gene from DNA into mRNA and translation of mRNA into a polypeptide (to ribosomes in the cell cytoplasm)
steps in gene expression
1|transcription
2|post-transcriptional modification
3|translation
4|post-translational modification
sense strand
the DNA strand that carries genetic information - used as the template in transcription (only one strand used)
anti-sense strand
not used as the template for transcription but the complementary free ribonucleotide triphosphates (ATP, GTP, CTP, UTP) attach to its unpaired nitrogenous bases
What is the enzyme that splits the DNA for gene expression called?
RNA polymerase
What happens to the DNA strands after gene expression is finished and the mRNA goes away?
they spontaneously join together again
promoter - terminator region
beginning of the gene (that is being expressed) - RNA polymerase recognizes it, attaches to it, and slides down, splitting the DNA until the terminator region (end of the gene)
steps of transcription in prokaryotes
1|initiation - RNA polymerase binds to the promoter region and unwinds and unzips the DNA (gene area)
2|elongation - RNA polymerase forms bonds between nucleotides - E is released from hydrolysis of 2 phosphate groups - polymerization in 5’ to 3’
3|termination - RNA polymerase reaches the terminator region (termination of the polymerization) - mRNA is complete so it gets released from the anti-sense strand and goes into cytoplasm - transcription in 5’ to 3’ direction
how are prokaryotic and eukaryotic DNA different regarding genes
prokaryotic is 99% genes and eukaryotic only 1-3% genes - most of it does not code for a heritable trait
exon
the coding part of a gene (codes for a heritable trait)
intron
the non-coding region within a gene - they will also be transcribed into the mRNA but will be removed from it later (and exons will be rejoined)
post-transcriptional modification
pre-mRNA gets turned into mature mRNA - introns are spliced out of the pre-mRNA with spliceosome - guanine is added to the 5’ and a poly-A tail to the 3’ end
enzyme which splices introns from the pre-mRNA
spliceosome
post-transcriptional modification in prokaryotes
doesn’t happen in prokaryotes (no introns), mRNA can be used straight away
what does the poly-A tail do to the mRNA
- aids in the transportation of mRNA into cytoplasm
- protects the mRNA from enzyme digestions
- aids in translation
(here because mRNA is not adjusted to the cytoplasm environment)
translation
process of polypeptide synthesis using mRNA as a guide (“mRNA gets turned into a polypeptide chain”)
how is mRNA organized (into what)
into triplets of N-bases called codons
One codon encodes…
But ___codon will encode __ amino acid.
…one amino acid. So for one tetrapeptide, twelve base pairs are required.
more than one, the same
start codon and start amino acid in all proteins
AUG, methionine
stop codons
codons that don’t code for any a-a - they signal the stop of the translation
Why do more codons code for the same a-a?
in case of a gene mutation (change in the base sequence), there is a lesser chance that the mutation will be transferred to the protein as well because there are more ways to reach the end a-a
central dogma of molecular biology
gene expression process always happens in the following way:
- DNA (gene) by transcription into mRNA
- mRNA by translation into a polypeptide chain
the only exceptions are retroviruses (their genes are in RNA so they get transcribed into DNA and then mRNA - reverse transcription)
genetic code
“translation dictionary” - which codons in the mRNA turn into which a-a
- it is universal (used by all species) and degenerate (some a-a are coded by multiple codons)
why is degeneration a positive trait?
it reduces the effect of mutations on protein structure/function - in case of a gene mutation (change in the base sequence), there is a lesser chance that the mutation will be transferred to the protein because there are more ways to achieve the a-a of interest (multiple codons code for it)
