Lecture 33: Loss of Heterozygosity

what is loss of heterozygosity

you have two copies of a gene but one is lost or inactivated so only one remains

• no longer heterozygous

what does loss of heterozygosity make you more prone of

prone to inherent a mutant gene because it is no longer masked by the normal allele

what is one example we’ve discussed that leads to loss of heterozygosity

crossover during homologous recombination because now both chromatids code for one frequency of the gene

does loss of heterozygosity always lead to a malfunction

no, it just means that there is a loss of allele frequency, even if you aren’t losing function protein

red: function

green: nonfunctional

both are still considered loss of heterozygosity

what is an example of loss of heterozygosity disease

retinoblastoma: eye tumor

what is the difference between replication and transcription

• replication requires both strands to be copied

• transcription has only one mRNA made bc only one DNA strand is copied

what is transcription

the synthesis of a single strand RNA transcript complementary to one strand of DNA of a gene

what are snRNAs

small nuclear RNAs - structural components of spliceosomes

whare are miRNAs

short single stranded RNAs that block expression of complementary mRNAs

what is the main difference between ribose and deoxyribose

ribose has a 2OH group whereas deozyribose has a 2H group, which makes ribose extremely unstable so it can’t code for anything genetic

what is the estimate amount of rRNA, tRNA, and mRNA in prokaryotes

more rRNA and tRNA becuase those can be recycled, mRNA is very small amount because it gets quickly degraded after it gets transcribed or else more proteins would constantly be made from the mRNA that we might now need

what other RNAs do eukaryotes have

• small nuclear RNA that are part of the splicisome complex and splices introns from RNA

• signal recognition particle: guides protein transport after translation to their designated areas

• microRNA that bind to mRNA after transcription and translation to induce degradation

• small interfering RNA as a result of viral infection and can bind to mRNA to induce degredation

• telomerase RNA which guides the synthesis of telomere with telomerase if we need to extend certain cells' chromosomes

what makes RNA and DNA polymerase different from each other

RNA polymerase can start adding bases without the need of a 3’ OH group

where does DNA unwinding usually start at

AT regions because this is where there are 2 h bonds, making it weaker and easier to break apart

in what direction does RNA polymerase transcribe

5 → 3, in the direction of the opening of the fork → how it knows which strand to use as the template

what does sigma subunit in the prokaryotic holoenzyme do

recognizes the promotor region on the DNA to start transcription

• it’s not part of the holoenzyme, it just guides the RNA polymerase to the promotor region and it knows where to go through cell signaling

what is the most common sigma subunit

sigma 70

what is upstream and downstream in transcription

going left, or toward the negative numbers is upstream (anything before start site of transcription) whereas going right toward positive number is downstream

explain the geography of prokaryotic gene

what does consensus sequence mean

it means it codes for the same thing, but has different variations

what are the two regions on the promotor that need to get recognized before transcription can occur for prokaryotes

-35 and -10, tata box

where is the TATA box in prokaryotes

in -10 region

what does transcription require

• template (DNA)

• rNTPs (what will build the mRNA through phosphodiester bonds linkage)

• metal ion (to shield the negative charges from each other like DNA polymerase)

how many RNA polymerase do eukaryotes have and what do they code for

Pol I: makes rRNA

pol II: makes mRNA

pol III: makes tRNA and small RNA

how many RNA polymerase do prokaryotes have

only one

do eukaryotic cells have a sigma for promotor recognition

no, it has transcription factors, proteins that can bind to DNA and serve similar roles in recognizing promotoes and activating transcription

what does the transcription of mRNA look like

• similar to DNA where it brings in rNTPs that are complement to the DNA bases and creates a phosphodiester bond between the bases so that it can link and become one chain

• always occur in a 5 → 3 direction

• only one strand if formed whereas in DNA, both strands are the template and then you end up with two