BIO EK CORRECT

Question 1

the formation of a dinucleotide is held by what bond?

Answer 1

• held by a phosphodiester bond
• due to the negative charges of the phosphate groups in the phosphodiester bond, nucleic acids are negatively charged (anions)–> making the DNA negative
• Histones, are proteins that are attached to DNA, and are positively charged & as a result are attracted to negatively charged phosphate groups

Question 2

HIGH YEILD MCAT FACT

Nucleolus is a dark circular structure that is respsonsible for the production of what?

Answer 2

• rRNA

Question 3

Which of several exceptions to mendelian inheritance?

Answer 3

• Codominance
  
  • example AB blood type, both alleles are expressed

Question 4

which eukaryotic cells DOES NOT display a nucleus?

Answer 4

• RBC
  
  • made in bone marrow
  • initially they have a nucleus, however, as RBC fill up with hemoglobin, the nucleus is pushed to the periphery of the cell & eventaully disappears
  • w/o a nucleaus RBC cannot divide
  • RBC survive ~ 120 days before they are degraded by the spleen, while bone marrow replenishes the supply

Question 5

Explain the concept that mitochondria rely on the nuclear mRNA for protein sythesis:

Answer 5

• mitochondria were once independent cells that were engulfed by a larger one, after many thousands of years, a SYMBIOTIC RELATIONSHIP has resulted between a mitochondrion & its host cell.
• as a result, a substantial percentage of mitochondrial proteins are dervied from nuclear mRNA

Question 6

PCR: polymerace chain reaction

Answer 6

• uses “primers” to copy & AMPLIFY specific regions of DNA
• DNA polymerase runs back & forth between the primers, copying the region of interest over & over again
  
  • by using PCR, s short stretch of DNA can be amplified a million times

Question 7

______________bond is used to link monosaccarides (i.e. glucose molecules)

__________is the formation of a spontaneous dipole moment that weakly attracts molecules toward each other

Answer 7

glycosidic bond

london dispersion

Question 8

to maintain the unzipping of the helix, SSBP attached to which nucleotide element during replication?

Answer 8

• attaches to the ssDNA, during replication and keeps the origin of replication open

Lets review the entire process:

1. Helicase is an ATP-dependent enzyme that “unzips” the DNA helix exposing the origin of replication
   
   1. if the DNA helix is not unzipped, DNA polymerases cannot replicate DNA
2. Once the origin of replication is open, it naturally wants to close back up, so the SSBPs prevents this from happening

Question 9

Human Somatic Cells

Answer 9

• they are not germ cells: like ova & sperm
• somatic cells is diploid (2N) and therefore houses 46 chromosomes
• chromosomes are further subdivded into 22 pairs of autosomes (these are numbered 1 through 22) & a pair of sex chromosomes (the female pair is XX & the male pair is XY)

Question 10

1. __________degree & type of DNA supercoiling is controlled by
2. ____________induces severe supercoiling when it unwinds DNA in order to expose the origin of replication
3. supercoiling is relieved by the actions of _________________, which induces breaks between nucleaotdies that relax DNA supercoils, and this action relieves the torisonal pressure that occurs during DNA replication & RNA synthesis

Answer 10

1. topoisomerases
2. helicases
3. gyrase (a type of topiosomerase)

• gyrase inhibitors: serve as antibiotics by inhibiting bacterial replication

Question 11

the genetic code is composed of 3 nucleotides coding for each amino acid. How many possible codons exist in nature that code for the 20 aa found in polypeptides?

Answer 11

• 64
  
  • 4 nucleaotides, 3 codons: 4³=64 possible codons for the 20 aa found in polypeptides (the genetic code is said to be redundant or degenerate because several different codons code for the same aa)
  • 61 codons code for aa 3 codons serve to terminate translation

Question 12

Autosomal Recessive: watch vidoe/notes Q 215