BIOL 104 Lecture Notes - Lecture 4: Murray Barr, Barr Body, Down Syndrome

104 views2 pages

brownreindeer350

13 May 2018

School

Department

Course

Professor

For unlimited access to Class Notes, a Class+ subscription is required.

Epigenetics:

So far, we have been discussing the flow of genetic information from DNA to RNA to Protein and how

mutations in the gene or promoter sequence can affect the function or the levels of the final protein.

This can lead to health issues because a protein should function in a specific cell type and at a specific

time.

However, these gene expression changes do not have to occur as a result of DNA mutation. Epigenetics

refers to genetic modifications that lead to physical variation without altering the nucleotide sequence.

As you know, a complex of transcription factors, along with RNA Polymerase, bind to

enhancers/silencers and the promoter to turn genes on or off. Recall the demonstration of a string

(DNA) wrapping around a finger (histones) that we had in lecture.

The positive charge of histones and the negative charge of the DNA allow both molecules to interact

really well. If the histone charge is “masked,” the DNA falls off the histone.

-The cell winds some regions of the genome tightly around histone proteins in order to shut a gene off.

If a region of the genome is tightly wound up, the transcriptional machinery cannot access the

promoter.

-The cell loosens DNA/histone complexes in some regions of the genome in order to turn a gene on. In

this case, the transcriptional machinery can easily access the promoter.

**The key moment in the switch in masking/demasking the histone charges is the methylation of DNA.

-DNA that is highly methylated is usually “off” and doesn’t make protein. -DNA that is not methylated is

usually “on” and does make protein.

I highlighted the craziness of this process by describing an extreme example of this…

X-inactivation -Males have 1 X chromosome -Females have 2 X chromosomes -Therefore, females have

double the number of X chromosome genes than males do.

This would be a problem for females because they would make double the amount of X chromosome

proteins. You already know what happens when there are too many copies of genes/proteins in a cell

(Down Syndrome, but more on that later). To combat this problem, females completely inactivate one

of their two X chromosomes in every cell in their body. The chromosome is so highly methylated that it

is wrapped tightly around histones to form a tiny dot under a microscope. This is called a Barr Body

because it was discovered by a dude named Murray Barr.

Epigenetics can help us explain how people develop health issues as they grow/age. This is particularly

true for monozygotic twins who are genetically identical. Why would two genetically identical people

have different personalities or susceptibilities toward disease? The answer could be epigenetics! -

Comparing the DNA methylation patterns of 3-year-old identical twins shows similarities. -Comparing

the DNA methylation patterns of 50-year-old identical twins shows many differences.

Therefore, DNA methylation/DNA packaging/gene expression changes occur as we grow/age. The

environment is known to play a role in modifying these DNA methylation patterns. In lecture, we

discussed two examples of environmental input shown to have this effect.

Unlock document

This preview shows half of the first page of the document.
Unlock all 2 pages and 3 million more documents.

Already have an account? Log in

Document Summary

So far, we have been discussing the flow of genetic information from dna to rna to protein and how mutations in the gene or promoter sequence can affect the function or the levels of the final protein. This can lead to health issues because a protein should function in a specific cell type and at a specific time. However, these gene expression changes do not have to occur as a result of dna mutation. Epigenetics refers to genetic modifications that lead to physical variation without altering the nucleotide sequence. As you know, a complex of transcription factors, along with rna polymerase, bind to enhancers/silencers and the promoter to turn genes on or off. Recall the demonstration of a string (dna) wrapping around a finger (histones) that we had in lecture. The positive charge of histones and the negative charge of the dna allow both molecules to interact really well.

Related Questions

QUESTION 10

If you can drink milk as an adult, it means that you have inherited a mutation in the promoter of your lactase gene (the gene that encodes the enzyme you need to break down lactose). Predict the effect of this mutation:

		The mutation changes the number of domains in the enzyme, which makes it work more efficiently
		The mutation changes the amino acid sequence of the lactase protein
		The mutation increases the number of copies of the lactase gene that will be found in your genome
		The mutation changes whether the lactase sequence is found in an intron or exon
		The mutation affects the expression of the lactase gene

1.2 points

QUESTION 11

A competitive inhibitor is decreasing the activity of an enzyme. Predict the effect of adding more substrate to the reaction.

		The substrate will increase the reaction rate by binding to the allosteric site
		The substrate will increase the reaction rate by competing with the inhibitor for the active site
		The reaction rate will not change unless the inhibitor can be removed
		The enzyme adjusts its shape so that the substrate, but NOT the competitive inhibitor, can bind
		The substrate will bind to the competitive inhibitor and block its ability to bind to the enzyme

1.2 points

QUESTION 12

What determines where in the genome a transcription regulator will bind?

		Transcription regulators bind to the 5' UTR region of a gene
		Regulators bind via complementary base-pairing to certain DNA molecules
		Covalent bonds form between the transcription regulator and the atoms of the DNA backbone
		Every eukaryotic gene has a different transcription regulator that will bind to the 5' end of the gene
		Transcription regulators bind to specific DNA sequences via multiple weak non-covalent interactions

1.2 points

QUESTION 13

What is the basic premise of cell theory?

		DNA -> RNA -> protein
		All cells arise from pre-existing cells
		DNA provides the complete instructions to create a cell
		The identity of a cell is determined through gene expression patterns
		All cells contain the same four basic macromolecules

1.2 points

QUESTION 14

What is the benefit of using BOTH the lac activator and the lac repressor to control gene expression?

		Using both an activator and repressor enables cells to more accurately determine the amount of lactose available in the environment
		Enzymes to digest lactose are only made when energy is low and lactose is available
		The activator can override the inhibition of the lac operon by the repressor
		The repressor can control the enhancer, while the activator can control the promoter
		When neither the lac activator or repressor is present, expression of the lac operon is too high

1.2 points

QUESTION 15

What is the histone code used for?

		Phosphorylation and acetylation of DNA affect its ability to be compacted
		Changes to the sequence of DNA change whether DNA will wrap around histone proteins
		Covalent modifications of histones affect the ability of the transcription initiation complex to form
		Histones provide the codon sequences needed for translation to occur
		The histone code affects which amino acids will get added to a polypeptide

2.)

a.) Are viruses that infect Archaea different from other bacterial viruses?

Yes, they do not have protein coats because of the extreme conditions where they live.

No, they consist of nucleic acid and protein just like other bacterial viruses.

Yes, the structure of archaeal viruses is always completely different from other bacterial viruses.

Yes, they have only DNA genomes.

b.) Of the following examples, which is not a common part of many viral life cycles?

The pox virus genome is replicated by DNA polymerase.

Adenoviruses attach to the cell and the nucleocapsid is taken up by the cell.

Pox viruses replicate in the cytoplasm of the cell.

Once an adenovirus virion is inside a cell, host RNA polymerases transcribe early genes

c.) Some viruses are associated with cancer. There are a variety of ways in which viruses may affect a cell in a way that may lead to cancer. Based on your knowledge of the life cycles of viruses and of molecular genetics, what is one way that this might happen?

Viral genetic material inserts into a host genome close to the termination sequence, far downstream of the promoter, and causes a silent mutation.

Viral genetic material inserts into a host genome in a repetitive noncoding region.

Viral genetic material inserts into a host genome, placing a promoter in a new location and turning on a gene that had previously been turned off.

Viral genetic material inserts into a host genome and causes a mutation in a promoter, turning off a gene that had previously been turned on.

d.) Which statement describes the difference between the normal neuron protein PrP^C and the pathogenic version PrP^Sc?

PrP^C is just a protein and the PrP^Sc is a protein with nucleic acid inside.

The PrP^C protein contains more beta sheets while the PrP^Sc protein contains more alpha helices.

The three-dimensional conformation is identical, but the amino acid sequence is different.

The amino acid sequence is identical, but the three-dimensional conformation is different.

1) In the wildtype (the DNA sequence most commonly found in nature) lac operon, transcription is severely down-regulated. A mutation in lacI that causes an early stop codon in the sequence (called a lacI - strain) results in an operon that has high levels of transcription of the polycistronic m-RNA. What type of regulatory protein is the LacI protein (hint: we covered this type of protein in lecture)?

The Lac regulatory protein is called a repressor. (is this correct)

2) If a bacterium with a wildtype lac operon is grown in the presence of lactose, high levels of transcription result for a while, however, eventually transcription is again down-regulated. If, on the other hand, the sugar IPTG is present (instead of lactose), transcription levels are high and remain high. What function do IPTG and lactose share? How are they differently affected by the operon product? (need help with this question)

Lactose and IPTG affected by the operon are both inducers of the Lac-Operon. (is this correct)

3) What is âepigeneticsâ? What forms of gene regulation are usually involved in epigenetic control of a trait? Why do we have such a limited understanding of epigenetic processes? (need help with this question)

Epigenetics is the study of phenotype changes that do not change the DNA sequence. Genes can be turned on and off based on environment situations of past generations, (parents or even grandparents) were exposed. Examples of some environmental factors could be diet, stress, smoking, drinking alcohol, and diseases. Histone modification and methylation are usually involved in epigenetic control of a trait. (is this correct)

BIOL 104 Lecture Notes - Lecture 4: Murray Barr, Barr Body, Down Syndrome

Document Summary

Get access

Related Documents

BIOL 104 Lecture Notes - Lecture 11: Mitosis, Independent Community And Health Concern, Trisomy

BIOL 104 Lecture Notes - Lecture 4: Sickle-Cell Disease, Point Mutation, Cytosine

BMS 150 Lecture Notes - Lecture 8: Small Nuclear Ribonucleoprotein Polypeptide N, Gland, Vaginal Cancer

Related Questions