genetics discussion 2 (transcription, slicing, mutations) Flashcards
1*. If DNA is double stranded, why do we say we have one copy of a gene in DNA, rather than 2?
- coding stand / 5 ==>3
- template strand / 3==>5
- mRNA / 5==>3
***in transcription, only one of the 2 DNA strands (template strand) is used to make RNA
***the template DNA strand (3to5)
==> make COMPLEMENTRY mRNA (5to3)
***RNA polymerase builds a mRNA stand in 5to3 direction/ adding ea new nucleotide to the 3 end of the template strand
= template strand used to make mRNA strand
*the template strand read the opposite direction to the coding, so that the mRNA can be made starting from 5==>3 (the same as the coding)
=mRNA is formed in the 5==>3 direction (this is the same direction of the coding strand)
2*. Explain how it is possible to get 3 different types of muscle proteins from just one gene.
= ALTERNATE SPLICING of the TROPOMYOSIN gene
***prod. several forma of alpha-tropomyosin mRNA
***introns are spliced out, leaving different exons in each mRNA strand, which code for diff types of protein (muscle tissues
- Although RNA is usually
* single stranded,
some viruses have
*double stranded RNA
as their genome.
(e.g. Rotavirus, the most common cause of infantile gastroenteritis in the world)
They need to bring
*RNA polymerase
with them when they infect a cell. Why can’t they use the RNA polymerase in human cells?
*VIRAL RNA polymerase can
ONLY transcribe
= from RNA
*HUMAN RNA polymerase transcribes
= from DNA
- HIV (Human immunodeficiency virus) has a coding strand of RNA. But instead of replicating, it can convert to DNA and hide in the DNA of the helper T-lymphocyte nucleus. Can it use enzymes in the host cell to convert to DNA?
NO
HIV bring along it’s own
= REVERSE TRANSCRIPTASE
which
CONVERST HIV RNA
= to DNA
*allowing it to HIDE in human DNA strand
***humans don’t have reverse transcriptase, bec> we don’t make DNA from RNA
- RNA polymerase only needs a promoter sequence to start making copies of mRNA, if the same polymerases are found in every cell why are different proteins produced in different cell types?
because transcription factors are required
these transcription factors are only produced when needed
- You are investigating a gene. You find it has a promoter sequence before the gene,
but it is very hard to find a time when the cell is producing a protein product from that gene. Why?
= bec…PARTICULAR CONDITIONS ARE REQUIRED to induce gene expression for that particular protein product.
It is necessary to REGULATE - cell DIFFERENTIATION - and GROWTH, this is achieved through CONTROL of GENE EXPRESSION
TRANSCRIPTION FACTORS
= can be ACTIVE ALL THE TIME, or
= ONLY UNDER PARTICULAR CONDITIONS
These transcription factors can be ACTIVATED IN A NUMBER OF WAYS.
These factors can be EXTRACELLUAR, or INTERACT WITH PROTEINS NEAR THE PROMOTOR which can SUPPRESS GENE EXPRESSION
Why are so many transcription factors required in a human cell?
Transcription factors are a TYPE OF REGULATORY PROTEINS.
So many are required in a human cell as they = REGULATE AND = INITIATE TRANSCRIPTION of genes, by BINDING TO A SPEC. REGION of DNA (DNA to RNA).
Transcription factors help ensure that the
=RIGHT GENES are expressed in the
=RIGHT CELLS of the body,
=at the RIGHT TIME
Give an example of when the body needs to
…suppress gene expression using a transcription factor.
Transcription factor is
eg…IMPORTANT IN TUMOUR SUPPRESSION as it
= ACTIVATES GENES for
1. GROWTH SUPPRESSION and
2. APOPTOSIS
Eg…
= interleukin 2 when expansion of lymphocytes is required to fight an infection.
=================
***Transcription factor binds to specific sequences of DNA to MODIFY TRANSCRIPTION
either
DIRECTLY (activator that binds to promoter region of DNA to start transcription) or INDIRECTLY (acting through cofactors)
Why physically can’t a strand of tRNA be used to encode a protein?
= bec…the physical STRUCTURE of tRNA is FOLDED
therefore the
***the ribosome cannot attach and start translating the strand of tRNA bec its folded up
***the folded strand has a 3D
L shape
due to NEUCLEOTIDE PAIRS forming on the molecule, making it bend
Why might the mRNA in the cytoplasm look different to the mRNA in a nucleus?
In Eukaryotes,
mRNA is SPLICED to REMOVE INTRONS before being transported to the cytoplasm.
nucleus = mRNA longer
cytoplasm - mRNA shorter
==> nucleus = pre-mRNA
==> nucleus = spliced to mRNA
==> cytoplasm = mature mRNA
Explain why a DNA mutation can still produce a protein that has the same sequence as a non-mutated gene?
= bec..
HD***genetic code is described as DEGENERATE (or redundant) because …
=a SINGLE AMINO ACID may be coded for by MORE THAN ONE CODON
=tf ***SILENT MUTATION…
CHANGE TO A CODON, BUT NO CHACE TO AMINO ACID PRODUCE
if a mutation was to happen and a nucleic acid was switched
it could still code for the same desired amino acid being adde to the polypeptide chain, NOT AFFECTING
- shape
- function
of end result
How can a mutation produce a smaller protein than normal?
==> mutation ==> leat to change in codon ==> wh can be a stop codon ==> signalling protein synthesis to end ==> protein cut short
Human ribosomes are
different from
bacterial ribosomes,
so antibiotics targeting protein production in bacteria are generally safe.
But some of these antibiotics can harm the mitochondria of human cells, why?
the RIBOSOME that mitochondria use for protein synthesis
is similar to those used by prokaryotic cells
mitochondria even having
DNA derived from
WHEN CELLS HAD PROKARYOTES INSIDE THEM
Some antibiotics function by binding to bacterial ribosomes and in some cases
==> MAY CONFUSE BACTERIAL RIBOSOME
==> with the RIBOSOMES OF MITOCHONRIA
Why does tRNA have an area called an anti-codon?
The area that is called the anti-codon on a tRNA
= contains 3 LETTERS that determines what AMINO ACID THAT GETS CARRIED.
This anti-codon sequence on the tRNA is
= COMPLEMENTARY TO THE mRNA sequence.
tRNA molecule is wobbly meaning that the anti-codon can bind to multiple bases
Which is likely to cause major changes in the protein produced by a gene? Explain why. A single base deletion or single base mutation? A one-base deletion or three-base deletion?
HD “FRAME SHIFT” = extra mark
= A SINGLE BASE DELETION would have the biggest effect
as it causes a
FRAME SHIFT
***by changing each of the codons (set of 3 ) that come after it, thus coding for different amino acids and changing the protein it then creates.
WA/ a SINGLE MUTATION or TRIPLE BASE DELETION would ==> ONLY IMPACT 1 CODON,
==> and therefore ONLY CHANGE 1 AMINO ACID
