Missed Bio/BCH MCAT

Question 1

____________ refers to inheretible phynotypic changes that occur through mechanisms other than alterations to the genome

Answer 1

Epigenetics refers to inheretible phynotypic changes that occur through mechanisms other than alterations to the genome

Question 2

Aneuploidy results from having too ____ or too ___ copies of a given chromosome.

Answer 2

Aneuploidy results from having too many or too few copies of a given chromosome.

• Note: Aneuploidy is typically discussed in meiosis, because that is where genetic changes are passed down to the progeny
  
  • However, Aneuploidy can also occur in mitosis which is a common occurence in cancer

Question 3

With which of the following do the arginine side chains found on histone proteins most likely interact?

Answer 3

Arganine = Basic (+)

DNA (sugar-phosphate backbone) –> phosphate (-)

Arg interact with the (-) charge on phosphate

Question 4

Activation of the Sympathetic nervous system causes _______ in the skeletal muscles and the ________ in the viscera.

Answer 4

Activation of the Sympathetic nervous system causes Vasodilation in the skeletal muscles and the Vasoconstriction in the viscera.

Question 5

Coenzymes that are tightly (or even covalently) bonded to their enzyme are known as ______________.

Answer 5

Coenzymes that are tightly (or even covalently) bonded to their enzyme are known as prosthetic groups.

Question 6

Vitamin __ plays a key role in vision, vitamin __ in calcium and phosphate absorption from the gastrointestinal tract, vitamin __ is an antioxidant, and vitamin __ promotes coagulation.

Answer 6

Vitamin A plays a key role in vision, vitamin D in calcium and phosphate absorption from the gastrointestinal tract, vitamin E is an antioxidant, and vitamin K promotes coagulation.

• Each of the vitamins is lipid soluble

Question 7

Trisomy ___, ___, and ___ are the only viable (survivable) trisomies

Answer 7

Trisomy 21, 18, and 13 are the only viable (survivable) trisomies

Question 9

What other way besides Km can we measure enzyme activity?

Answer 9

(Ka) can also be defined, using the mathematical formalism of equilibrium constants, as [ES]/[E][S], where [ES] is the concentration of the enzyme-substrate complex, [E] is the concentration of the enzyme, and [S] is the concentration of the substrate. The dissociation constant (Kd) is then the inverse of Ka, and can be defined as [E][S]/[ES].

Question 10

Relate Arachadonic acid and Prostoglandins to one another

Answer 10

Prostaglandins are signaling lipids that work via autocrine/paracrine signaling

Arachadonic acid is the precusror that makes prostoglandins

the main function of prostaglandins is to regulate cAMP (secondary messenger)

Question 11

Explain the process of transcription

Answer 11

The DNA helix must be unzipped for transcription to take place, which means that some of the same machinery used for DNA replication has to be engaged, especially enzymes like helicase and topoisomerase. RNA polymerase is the enzyme responsible for RNA synthesis. In eukaryotes, it binds to a promoter region upstream of the start codon with the assistance of transcription factors, the most important of which is the TATA box. RNA polymerase travels along the template strand in the 3’-5’ direction, synthesizing an antiparallel complement in the 5’-3’ direction. The template strand is known as the antisense strand, and the opposite strand is known as the sense strand, because it corresponds to the codons on the mRNA that is eventually exported to the cytosol for translation.

Question 12

Explian what happens to a RNA transcript immediatly after it has been transcribed

Answer 12

The immediate product of transcription in eukaryotes is not mRNA, but heterogeneous nuclear RNA (hnRNA). hnRNA must undergo a set of post-transcriptional modifications to become mRNA. Examples commonly tested on the MCAT include the 3’ poly-A tail, the 5’ cap, and splicing. The 3’ poly-A tail is a string of approximately 250 adenine (A) nucleotides added to the 3’ end of an hnRNA transcript to protect the eventual mRNA transcript against rapid degradation in the cytosol. The 5’ cap refers to a 7-methylguanylate triphosphate cap placed on the 5’ end of an hnRNA transcript. Similarly to the 3’ poly-A tail, it helps prevent the transcript from being degraded too quickly in the cytosol, but it also prepares the RNA complex for export from the nucleus.

In splicing, noncoding sequences (introns) are removed and coding sequences (exons) are ligated together. (Remember that exons are expressed).

Each gene normally has multiple distinct exons that can be ligated in different combinations; that is, if a gene had a set of four exons named A, B, C, and D, possible alternate splicing combinations could include ABCD, ABC, ACD, ABD, BCD, and so on.

This dramatically increases the amount of different, but related proteins that can be expressed from a single gene. Splicing explains why there are over 200,000 proteins in the human body, but only approximately 20,000 genes. Splicing is carried out by the spliceosome, a combination of small nuclear RNAs (snRNAs) and protein complexes.

Question 13

What role does the Gallbaldder play in the Digestive system and what sort of abnormailty would you expect to see in someone who had a colycystectomy?

Answer 13

The Gallbladder hold bile that is secreted from the liver and removing it might cause higher level of fa in a person (becuase the role of bile salts is to help in the digestion/absorbtion of fats)

Question 14

Ethylene (C2H4) is a gas, how would it cross a membrane?

Answer 14

Facilitated diffusion