BCH exam 2 practice questions

What is the difference between a nucleobase and a nucleoside and a nucleotide

A nucleobase is only the base; a nucleoside is base plus sugar; a nucleotide is nucleoside plus one or more phosphates

What two features distinguish RNA nucleotides from DNA nucleotides

RNA has a 2-prime hydroxyl and usually contains uracil; DNA has a 2-prime hydrogen and contains thymine

What is the charge of uracil at pH 7

Uracil has a net charge of zero

Why is DNA more stable than RNA under alkaline conditions

RNA has a 2-prime hydroxyl that can attack its backbone and form a cyclic intermediate; DNA lacks this hydroxyl

What does it mean that DNA is metastable

DNA hydrolysis is thermodynamically favorable but occurs extremely slowly without a catalyst

In the sequence 5-prime GATTACA 3-prime what bases are at the two ends

G is at the 5-prime end and A is at the 3-prime end

What is the difference between DNA secondary and tertiary structure

Secondary structure includes the double helix; tertiary structure includes long-range folding such as supercoiling

What technique revealed the DNA double helix and who generated the key data

X-ray diffraction using data generated by Rosalind Franklin

How many hydrogen bonds connect AACCCGGGTTTT to its complementary strand

Thirty hydrogen bonds

What interactions stabilize double-stranded DNA

Hydrogen bonding and base stacking and phosphodiester bonds and positive ions that reduce phosphate repulsion

How did the Meselson-Stahl experiment support semiconservative replication

Nitrogen-15 and nitrogen-14 produced density patterns showing each daughter DNA had one old strand and one new strand

What are the main properties of A-DNA and B-DNA and Z-DNA

A-DNA occurs in DNA-RNA hybrids; B-DNA is the common cellular form; Z-DNA is left-handed

Which enzyme can change the linking number of DNA

DNA gyrase which is a type of topoisomerase

What does a DNA 260 over 280 ratio of 0.89 suggest

The sample likely contains substantial protein contamination

How are DNA fragments ordered from least far to farthest on an agarose gel

Longest fragments travel least far and shortest fragments travel farthest toward the positive electrode

What are the two main immune responses

Innate immunity is fast and nonspecific; adaptive immunity is specific and develops memory

What are humoral immunity and cell-mediated immunity

Humoral immunity uses B cells and antibodies; cell-mediated immunity uses T cells against infected or abnormal cells

What are the five immunoglobulin classes and which is most common

The classes are IgM IgD IgE IgA and IgG; IgG is the most abundant in circulation

What is the basic structure of IgG

IgG has two identical heavy chains and two identical light chains with two Fab regions and one Fc region

Which amino acid forms the bonds holding antibody chains together

Cysteine forms disulfide bonds

What are the functions of antibody variable and constant regions

The variable region recognizes a specific epitope; the constant region interacts with immune effector components

Which region determines the shape and charge of an antigen-binding site

The hypervariable region which is also called the complementarity-determining region

What forces stabilize antigen-antibody binding

Hydrogen bonds and ionic interactions and van der Waals forces and hydrophobic interactions

How do myoglobin and hemoglobin differ

Myoglobin is a monomer that stores oxygen in tissues; hemoglobin is a tetramer that transports oxygen in blood

What chains form adult hemoglobin and what distinguishes a holoprotein from an apoprotein

Hemoglobin has two alpha and two beta chains; a holoprotein contains heme while an apoprotein lacks heme

What residue stabilizes oxygen in the myoglobin binding pocket

The distal histidine stabilizes oxygen through hydrogen bonding

What does a low P50 indicate

A low P50 indicates high oxygen affinity and less efficient oxygen unloading

What are the T and R states of hemoglobin

The T state is deoxygenated with low affinity; the R state is oxygenated with high affinity

What is positive cooperativity in hemoglobin

Binding one oxygen molecule increases the affinity of the remaining oxygen-binding sites

What is the difference between homotropic and heterotropic effectors

A homotropic effector is the normal ligand; a heterotropic effector binds at a different regulatory site

Which molecules are negative heterotropic effectors of hemoglobin

Hydrogen ions and carbon dioxide and chloride and 2 3-BPG decrease oxygen affinity

How do silent and missense and nonsense and frameshift mutations differ

Silent does not change the amino acid; missense changes one amino acid; nonsense creates an early stop; frameshift changes the downstream reading frame

What is the difference between lock-and-key and induced fit

Lock-and-key assumes a preformed active site; induced fit involves a conformational change after substrate binding

How does competitive inhibition affect Km and Vmax

Km increases while Vmax remains unchanged

Which inhibition occurs when the inhibitor binds only the ES complex

Uncompetitive inhibition; both apparent Km and Vmax decrease

How does pure noncompetitive inhibition affect Km and Vmax

Km remains unchanged while Vmax decreases

How does mixed inhibition affect Km and Vmax

Vmax decreases while Km may increase or decrease

What are the slope and intercepts of a Lineweaver-Burk plot

The slope is Km over Vmax; the y-intercept is 1 over Vmax; the x-intercept is negative 1 over Km

For y equals 0.0266x plus 0.0668 what are Vmax and Km

Vmax is about 14.97 mM per second and Km is about 0.398 mM

If velocity is 80 mM per second with substrate 12 mM and Km 3 mM what is Vmax

Vmax is 100 mM per second

If Km is 5 mM and kcat is 11 per second and enzyme is 9 mM and substrate is 11 mM what is velocity

Velocity is about 68.06 mM per second

If velocity is 14 mM per second and Km is 2 mM and enzyme is 6 mM and substrate is 10 mM what is kcat

kcat is 2.8 per second

What is the order of the slow ES to product step

It is first order with respect to the ES complex

Enzyme A has kcat 13 and Km 4 while enzyme B has kcat 10 and Km 5 which is more efficient

Enzyme A because its kcat over Km is 3.25 compared with 2 for enzyme B

Enzyme S has kcat 15 and Km 5 while enzyme T has kcat 5 and Km 18 which is more efficient

Enzyme S because its kcat over Km is 3 compared with about 0.278 for enzyme T

Enzyme C has kcat 12 and an uncatalyzed rate of 2 while enzyme G has kcat 4 and an uncatalyzed rate of 1 which has greater rate enhancement

Enzyme C because its enhancement is 6 compared with 4 for enzyme G

What does a higher kcat over Km value mean

The enzyme converts substrate to product more efficiently especially at low substrate concentration

What is the stereochemical relationship between D-galactose and D-glucose

They are C4 epimers and therefore diastereomers

How are Fischer substituents transferred into a Haworth projection for a D-sugar

Groups on the right point down and groups on the left point up

How are alpha and beta D-sugars identified

Alpha has the anomeric hydroxyl down; beta has the anomeric hydroxyl up

What is the relationship between the alpha and beta forms of the same sugar

They are anomers that differ only at the anomeric carbon

What is the structure of sucrose and is it reducing

Sucrose is glucose alpha 1 to 2 beta fructose and is nonreducing because both anomeric carbons are linked

What is the structure of maltose and is it reducing

Maltose is glucose alpha 1 to 4 glucose and is reducing because one anomeric carbon remains free

What makes a carbohydrate a reducing sugar

A reducing sugar has a free anomeric carbon that can open into a carbonyl form

What antigens and antibodies occur in the four ABO blood types

Type A has A antigen and anti-B; type B has B antigen and anti-A; type AB has both antigens and no antibodies; type O has neither antigen and both antibodies

Which carbohydrate is the repeating monomer of chitin

N-acetyl-beta-D-glucosamine connected through beta 1 to 4 bonds

How can a uronic acid be recognized

Its terminal primary alcohol has been oxidized to a carboxylate or carboxylic acid

How can a ketose be recognized

It contains an internal ketone carbonyl rather than a terminal aldehyde

What is lactose made of and is it reducing

Lactose is galactose beta 1 to 4 glucose and is a reducing sugar

Which carbon normally begins a glycosidic linkage

The donor sugar uses its anomeric carbon which is carbon 1 in aldoses and carbon 2 in ketoses