Biochemistry and medical genetics

Question 1

Definition of transcription

Answer 1

transfer of information from DNA to RNA

Question 2

Definition of translation

Answer 2

transfer of information in the RNA base sequence to the amino acid sequence of a protein (RNA → PROTEIN)

Question 3

In what phase does DNA replication occur

Answer 3

S-phase

Question 4

Definition of the M phase

Answer 4

it is the time in which the cell divides to form 2 daughter cells

Question 5

Definition of Interphase

Answer 5

Describes the time between 2 cell divisions of mitoses

Question 6

T/F: Gene expression occurs throughout all stages of interphase

Answer 6

True

Question 7

How is Interphase divided and what does happens in each of those phases

Answer 7

G0: cells that have stopped cycling, such as muscle and nerve cells, are said to be in this state

G1 phase (gap 1): cellular growth preceding DNA synthesis

S phase (DNA synthesis): DNA replication occurs
- at the end of S phase each chromosome has doubled its DNA content and is composed of 2 identical sister chromatids linked at the centromere

G2 phase (gap 2): period of cellular growth after DNA synthesis but preceding mitosis. Replicated DNA is checked for any errors before cell division

Question 8

What phase of the cell cycle target the following chemotherapeutic agents: methotrexate, 5-fluoruoracil and hydroxyurea

Answer 8

S phase

Question 9

What phase of the cell cycle target the following chemotherapeutic agents: bleomycin

Answer 9

G2 phase

Question 10

What phase of the cell cycle target the following chemotherapeutic agents: paclitaxel, vincristine, vinblastine

Answer 10

M phase

Question 11

What phase of the cell cycle target the following chemotherapeutic agents: cyclophosphamide, cisplatin

Answer 11

They are non cell-cycle specific

Question 12

What are the names of the proteins that ensure that cells will not enter the next phase of the cycle until the molecular events in the previous cell cycle phase are concluded

Answer 12

cyclins and cyclin-dependent kinases

Question 13

T/F: Reverse transcription is more commonly associated w/ life cycles of retroviruses

Answer 13

True

Question 14

What are nucleic acid assembled from?

Answer 14

nucleotides, which consist of 3 components:

• nitrogenous base
• 5 carbon sugar (pentose)
• phosphate

Question 15

What are the 2 types of nitrogen-containing bases commonly found in nucleotides?

Answer 15

purines and pyrimidines

Question 16

structural characteristics of purines

Answer 16

they contain 2 rings in their structure

Question 17

what are the purines commonly found in nucleic acids

Answer 17

adenine and guanine

Question 18

structural characteristics of pyrimidines

Answer 18

have only 1 ring

Question 19

What are the pyrimidines? commonly found in nucleic acids

Answer 19

Cytosine (DNA & RNA)
Thymine (DNA)
Uracil (RNA)

Question 20

What is the pyrimidine that is only found in RNA

Answer 20

Uracil

Question 21

What is the pyrimidine that is only found in DRA

Answer 21

Thymine

Question 22

How are nucleosides formed

Answer 22

They are formed by covalently linking a base to the number 1 carbon of a sugar

Question 23

How are nucleotides formed

Answer 23

They are formed when 1 or more phosphate groups is attached to the 5 carbon nucleoside

Question 24

T/F: In Nucleic Acids, a phosphate group links the 3’ carbon of a sugar to the 5’ carbon of the next sugar (3’, 5’ phosphodiester bonds) and have distinct 3’ and 5’ ends, thus polarity

Answer 24

TRUE

Question 25

T/F: Nucleic Acids sequence is always specified 3' → 5'

Answer 25

False! | It is always specified as 5' → 3'

Question 26

What are the properties ofChargaff's rules

Answer 26

The amount of A equals the amount of T, and the mound of G equals the amount of C. Thus, total purines equals total pyrimidines

Question 27

What does Adenine pair with and with how many hydrogen bonds

Answer 27

Thymine (w/ DNA) ... Uracil (w/ RNA) | and with 2 hydrogen bonds

Question 28

What does Guanine pair with and with how many hydrogen bonds

Answer 28

Cytosine | and with 3 hydrogen bonds

Question 29

What can cause a double-helical DNA to be denatured

Answer 29

Conditions that disrupt hydrogen bonding and base stacking (no covalent bonds are broken in this process) Heat, alkaline pH, and chemicals such as formamide and urea are commonly used to denature DNA

Question 30

Can denatured single-stranded DNA be renatured?

Answer 30

Yes, if the denaturing condition is slowly removed

Question 31

What enzymes can change the amount of supercoiling in DNA molecules

Answer 31

Topoisomerases

Question 32

what is negatively supercoiled DNA

Answer 32

DNA that is wound more loosely than in Watson-Crick DNA. This form is required for most biologic reactions

Question 33

What is positively supercoiled DNA

Answer 33

DNA is wound more tightly than in Watson-Crick DNA

Question 34

What is the basic packing unit of chromatin

Answer 34

nucleosome

Question 35

What are nucleosomes made of and what function does Histone H1 have?

Answer 35

- 2 copies of histones: H2A, H2B, H2, and H4 (they aggregate to form the histone octamer that the DNA wraps around - a series of nucleosomes is sometimes called "beads on a string" but is more properly referred to as a 10nm chromatin (it is more "opened" than the 30nm fiber) - Histone H1 is associated with the linker DNA found between nucleosomes to help package them into a solenoid-like structure, which is a thick 30nm fiber

Question 36

What are the types of chromatin that cells in interphase have?

Answer 36

Euchromatin: more opened and available for gene expression Heterochromatin: much more highly condensed and associated w/ areas of the chromosomes that are not expressed

Question 37

During what phase of the cell cycle is the chromosome structure visible

Answer 37

Mitosis

Question 38

``` Endonuclease activation and chromatin fragmentation are characteristic features of eukaryotic cell death by apoptosis. Which of the following chromosome structures would most likely be degraded first in the apoptotic cell? A) Barr body B) 10nm-fiber C) 30nm-fiber D) Centromere E) Heterochromatin ```

Answer 38

B) 10nm-fiber - the more "opened" the DNA, the more sensitive it is to enzyme attack. The 10-nm fiber, w/o the H1, is the most open structure listed. The endonuclease would attack the region of unprotected DNA between the nucleosomes

Question 39

``` A medical student working in a molecular biology laboratory is asked by her mentor to determine the base composition of an unlabeled nucleic acid sample left behind by a former research technologist. The result of her analysis showed 10% adenine, 40% cytosine, 30% thymine, and 20% guanine. What is the most likely source of the nucleic acid in this sample? A) Bacterial chromosome B) Bacterial plasmid C) Mitochondrial chromosome D) Nuclear chromosome E) Viral genome ```

Answer 39

E) Viral genome - a base compositional analysis that deviated from Chargaff's rules (%A=%T, %C=%C) is indicative of single-stranded, not double-stranded, nucleic acid molecule. All options listed except E are examples of circular or linear DNA double helices. Only a few viruses (Ex: parvovirus) have single-stranded DNA