Test 3 study guide

Question 1

Is the regulation of gene expression more complicated in eukaryotes or prokaryotic cells? Why?

Answer 1

It is more complicated in eukaryotes because the cells are more complex, the nuclear DNA is organized with histones into chromatin and multicellular eukaryotes produce large numbers and different types of cells

Question 2

WHy are eukaryotes more complex than prokaryotes?

Answer 2

They have a nucleus, mitochondria, and many proteins that must be coded for

Question 3

What are the four steps of steps of gene regulation in eukaryotes?

Answer 3

1. Transcriptional control
2. Post-transcriptional control
3. Translational control
4. Post-translational control

Question 4

What happens during the transcriptional control in eukaryotes?

Answer 4

Proteins called transcriptional factors recognize and bind to the TATA box and then recruit RNA polymerase. The activator binds to the enhancer and results in a max level of transcription

Question 5

What are the 5 steps of Transcriptional control?

Answer 5

1. General transcription factors
2. Activators
3. DNA Methylation
4. Histone tail acetylation
5. Chromatin remodeling

Question 6

What happens during general transcription factor step?

Answer 6

General transcription factors on their own will generate a low-level of expression, the more there are, the higher the expression of the gene

Question 7

What happens during activator in Transcriptional control?

Answer 7

Activators are proteins that bind to the promoter proximal elements and cause a high transcription rate. Other activators can bind to the enhancer region and form a multi-protein complex with activators at the promoter proximal elements, causing a maximum rate expression

Question 8

What happens during DNA methylation during transcriptional control ?

Answer 8

Adds a methyl group onto the bases in the DNA. methylated bases in promoter regions can prevent the binding of transcription factors which turns off the gene

Question 9

What happens during histone tail acetylation in the transcriptional control?

Answer 9

It chnages the charge of the histone tails and results in a loosening of the association of the histones with the DNA

Question 10

What happens during chromatin remodeling in transcritpional control?

Answer 10

Chromatin can be remodeled to make the promoter accessible to transcriptional factors and activators, increasing the transcription rate.

Question 11

What are the three steps in Post-Transcriptinal control

Answer 11

1. 5’ cap
2. Poly (À) tail
3. Splicing/ alternative splicing

Question 12

What happens during the 5’ cap process? And how is it made?

Answer 12

It contains 3 phosphate group and a guanine. It protects the mRNA from degredation and it is where ribosomes attach at the start of translation

Question 13

What happens during the Poly(A) tail process ?

Answer 13

The Poly(A) tail prevents degredation of mRNA when it enters the cytoplasm

Question 14

What happens during the process of splicing/alternative splicing?

Answer 14

Exon shuffling occurs. It is a great advantage because it generates protein diversity. They can produce different isoforms with the same gene

Question 15

What is the step occurring during the translational control?

Answer 15

1. Adjustment of Poly(A) tail

Question 16

What happens during the process of the Poly(A) tail adjustment?

Answer 16

It has an effect of increasing translation or decreasing translation depending on if we increase or decrease the length of the Poly(A) tail prevents degredation

Question 17

What are the three steps occurring during Post-Translational control?

Answer 17

1. Processing (Protein activation)
2. Polyubiquitination
3. Proteasome

Question 18

What happens during the processing process ?

Answer 18

Proteins are synthesized as inactive precursors, which are converted to an active form under regulatory control

Question 19

What happens during the polyubiquitin process in post-translational control?

Answer 19

It adds ubiquitin to the protein which helps tag the doomed (short-lived) protein

Question 20

What happens during the proteasome process in post-translational control?

Answer 20

Ubiquitin tags identifies the doomed proteins so they can get attacked by proteasome

Question 21

How would you configure the following elements of eukaryotic gene regulation to cause the highest quantity of active insulin cell?

Answer 21

Many general transcription factors, many activators on promoter proximal elements, many activator on enhancer region, no gene methylation, histone tail acetylation, promoter available for chromatin remodeling, 5’ cap, should have a poly(A) tail, introns should be removed by slicing, Poly(A) tail should be long, processing should occur, no poly ubiquitin and proteasome

Question 22

How would you configure the following elements of eukaryotic gene regulation to cause the lowest quantity of active insulin in a cell?

Answer 22

No général transcription factors, no activators on promoter proximal elements, no activators on enhancer region, gene methylation, no histone tail acetylation, no chromium remodling, no 5’ cap, no Poly (A) tail, introns should not be removed, a short Poly (A) tail, no processing, polyubiquitination present, present of proteasome

Question 23

How do polysomes increase the rate of transmission of a single mRNA?

Answer 23

Since the polysome generates multiple ribosomes that simultaneously translate a single mRNA. Multiple ribosomes attach at the same mRNA at different points and begin translating it at different points along its length, producing more copies of proteins in a shorter amount of time. As one ribosome moves along and completes translation, another can immediately begin translating from the same mRNA. They read from 5’ to 3’.

Question 24

How is the expression of housekeeping genes different from genes expressed only in particular cell types.

Answer 24

Housekeeping genes are genes expressed in all cell types for basic cellular functions such as glucose metabolism. They have promoter proximal elements that are recognized by activators present in all cell types. Compared to gene expressed only in particular cell types have promoter proximal elements that are recognized by specialized activators or at specific times when transcription of genes needs to be activated.

Question 25

How does DNA methylation, histone tail acetylation and chromatin remodeling regulate gene expression?

Answer 25

DNA methylation enzyme adds a methyl group onto bases in the DNA. Methyled bases in the promoter regions can prevent the binding of transcription factors turning off the gene, Acetylation changes the charge of the histone tails and results in a loosening of the association of the histone with the DNA. This change is called chromatin remodelling where the gene transcription factors and RNA polymerase II are free to bind and initiate transcription.

Question 26

How does the 5’cap and the poly-A tail help with the translation of a mRNA molecule?

Answer 26

The 5’ cap protects the mRNA from degradation and is the site where ribosomes attach at the start of translation. Near the 3’ end, a DNA sequence is transcribed into the pre-mRNA. Protein binds to this polyadenylation signal in the RNA. This signals the RNA polymerase to stop transcription. Then the enzyme poly(A) polymerase adds a chain of adenine nucleotides to the newly created end of the pre-mRNA.

Question 27

How does alternative splicing contribute to protein diversity and serve different functions in the cell?

Answer 27

Alternative splicing allows exon shuffling which generates protein diversity, but it can also lead to disorders. The exons can be assembled in different combinations to produce different isoforms with the same gene. However, depending on the arrangement, it could lead to disorder.

Question 28

How is the lifespan of proteins regulated in a cell ?

Answer 28

Proteins are broken down by a system called the proteasome. Some proteins such as collagen last a life time whereas others are short lived. The short lived proteins involved in regulatory organism are marked for breakdown by enzymes that attach a doom tag which consists of a small protein called ubiquitin. The ubiquitin tags labels the doomed protein so that they are recognized and attacked by a proteasome.

Question 29

Compare and define Lamarck’s and Darwin’s theories of evolution.

Answer 29

Lamarck proposed that a metaphysical “perfecting principal” caused organisms to become better suited to their environments. Larmarkism theory consists of the transmission of acquired traits within a lifetime. Therefore, simple organism evolved into more complex ones. He based himself on two principle
1. Principle of use and disuse that infers that body parts grow in proportion to how much they are used
2. unused structures get weaker and shrink
Darwin on his side noticed that the animals and plants on different islands varied slightly in form. By studying flinches, he came to the conclusion that species were adapted to their environment. Both came to the conclusion that organism change in response to their environment, Lamarck believed that acquired traits could be passed down, while Darwin proposed that natural selection was the primary mechanism of evolution

Question 30

What is natural selection?

Answer 30

Darwin defines natural selection as being the principle by which each slight variation of a trait, if useful, is preserved. It is the process by which characteristics that better enable organisms to adapt to specific environmental pressures will tend to increase in suceeding generations. Those organism will then be better able to survive and reproduce. This is all done by nature and is called fitness.

Question 31

Explain how the weaknesses of the original theory of evolution proposed by Darwin are addressed/solved by the modern theory of evolution (neo-Darwinism/modern synthesis).

Answer 31

4 weakness of his theory are:
1. Natural selection is not the only mechanism at work in evolution
2. Darwin didn’t provide the mechanism of inheritance explaining the theory
3. Darwin proposed that the evolution was gradual, but there is often a lack of intermediary fossils
4. It is still hard to explain the molecular details of reproductive isolation
How are they addressed and solved:
Modern synthesis integrates data from biogeography, comparative morphology and others. Although it considers natural selection the primary mechanism of evolution, modern synthesis acknowledged the importance of other process such as microevolution and macroevolution.

Question 32

Compare and differentiate microevolution and macroevolution, recognize and give examples for each.

Answer 32

Microevolution describes the small-scale genetic change that populations undergo, often in response to shifting environmental circumstances. An example would be a small evolutionary shift in the size of the bill of a Galapagos finch. Macroevolution on the other hand describes a larger-scale evolutionary changes observed in species. It results in the gradual accumulation of microevolutionary changes that leads to speciation. The accumulation of all microevolution lead to the differentiation of species between coyotes, gray wolf and a dog

Question 33

Explain how genetic drift contrasts to natural selection in the selection of alleles.

Answer 33

Genetic drift is a random process that causes allele frequencies to change purely by chance. Unlike natural selcetion, genetic drift does not favor any particular allele based on its beneficial or harmful effects. Natural selection is a non-random process where certain alleles become more common in a population because they confer a survival or reproductive advantage. Natural selection works on alleles that affect an organism’s fitness, which is its ability to survive and reproduce in a particular environment. Alleles that increase an organism’s fitness are more likely to be passed on to the next generation, while those that decrease fitness are less likely to be passed on.
Differences:
1. Mechanism: Genetic drift is random and does not consider allele fitness, while natural selection is non-random and directly tied to the advantage or disadvantage of an allele in the given environment.
2. Outcome: Genetic drift can result in the fixation or loss of alleles regardless of whether they are beneficial or harmful, while natural selection leads to the spread of beneficial alleles and the elimination of harmful ones.

Question 34

Provide a comprehensive explanation of why diversity in a gene pool is important for the survival of a species, its adaptation and its evolution.

Answer 34

A gene pool consists of the genetic diversity within a population. A large gene pool indicates extensive genetic diversity, increased chances of biological fitness, which is associated with robust population that can survive bouts of intense selection. Low genetic diversity reduces biological fitness and an increased chance of extinction. A diverse gene pool increases the likelihood that some individuals in the population have traits that make them resistant to various environmental change since if there is an environmental change, not all the population gets wiped out but only those who are not adapted to the environment. If all individuals in a population were genetically identical, no variation would exist for natural selection to favor, and the species could not adapt to changing environments. A diverse gene pool means that the population is more likely to have the necessary genetic variations that will allow individuals to adapt to new challenges. Over long periods, genetic diversity can lead to speciation (the formation of new species). When populations of the same species become isolated from one another. If there is a broad genetic diversity, the chance that important alleles will be lost is minimized (against genetic drift).

Question 35

What are the five agents of microevolution?

Answer 35

1. Mutation
2. Non-random mating
3. Gene flow
4. Genetic drift
5. Natural selection