1.12. Expression of genes - transcription

Question 1

polygenic vs monogenic inheritance

Answer 1

monogenic - the trait results from the expression of only one gene (or one gene pair)
polygenic - results from the expression of multiple genes

Question 2

gene

Answer 2

a part of DNA with a specific base-sequences that code for the a-a sequence of one polypeptide chain

Question 3

gene expression

Answer 3

transcription of a gene from DNA into mRNA and translation of mRNA into a polypeptide (to ribosomes in the cell cytoplasm)

Question 4

steps in gene expression

Answer 4

1|transcription
2|post-transcriptional modification
3|translation
4|post-translational modification

Question 5

sense strand

Answer 5

the DNA strand that carries genetic information - used as the template in transcription (only one strand used)

Question 6

anti-sense strand

Answer 6

not used as the template for transcription but the complementary free ribonucleotide triphosphates (ATP, GTP, CTP, UTP) attach to its unpaired nitrogenous bases

Question 7

What is the enzyme that splits the DNA for gene expression called?

Answer 7

RNA polymerase

Question 8

What happens to the DNA strands after gene expression is finished and the mRNA goes away?

Answer 8

they spontaneously join together again

Question 9

promoter - terminator region

Answer 9

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)

Question 10

steps of transcription in prokaryotes

Answer 10

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

Question 11

how are prokaryotic and eukaryotic DNA different regarding genes

Answer 11

prokaryotic is 99% genes and eukaryotic only 1-3% genes - most of it does not code for a heritable trait

Question 12

exon

Answer 12

the coding part of a gene (codes for a heritable trait)

Question 13

intron

Answer 13

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)

Question 14

post-transcriptional modification

Answer 14

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

Question 15

enzyme which splices introns from the pre-mRNA

Answer 15

spliceosome

Question 16

post-transcriptional modification in prokaryotes

Answer 16

doesn’t happen in prokaryotes (no introns), mRNA can be used straight away

Question 17

what does the poly-A tail do to the mRNA

Answer 17

• 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)

Question 18

translation

Answer 18

process of polypeptide synthesis using mRNA as a guide (“mRNA gets turned into a polypeptide chain”)

Question 19

how is mRNA organized (into what)

Answer 19

into triplets of N-bases called codons

Question 20

One codon encodes…
But ___codon will encode __ amino acid.

Answer 20

…one amino acid. So for one tetrapeptide, twelve base pairs are required.
more than one, the same

Question 21

start codon and start amino acid in all proteins

Answer 21

AUG, methionine

Question 22

stop codons

Answer 22

codons that don’t code for any a-a - they signal the stop of the translation

Question 23

Why do more codons code for the same a-a?

Answer 23

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

Question 24

central dogma of molecular biology

Answer 24

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)

Question 25

genetic code

Answer 25

“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)

Question 26

why is degeneration a positive trait?

Answer 26

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)