MCAT Biochemistry: Nucleotides, Carbohydrates, & Lipids

how do histones associate with DNA

by forming salt bridges between positively charged amino acid residues and negatively charged phosphate groups

how does acetylation of lysine residues in histones increase gene expression

the salt bridges between charged amino acids and phosphate groups are disrupted

epimers

differ at only one stereocenter

anomers

differ only at the anomeric carbon

what do peptide hormones require

a second messenger

do steriod hormones require a second messenger

no

prostaglandins

20-carbon non-hydrolyzable lipids that act as autocrine and paracrine signals (act only on nearby cells)

terpenes

precursors in the synthesis of cholesterol and steroid hormones

ketone bodies

fuel sources that are produced under low glucose conditions

catecholamines

hormones derived from the amino acid tyrosine, generally act as endocrine signals

reducing sugars

have hemiacetal or hemiketal configurations at their anomeric carbon

nonreducing sugars

have acetal or ketal configurations at their anomeric carbon

where are triglycerides found

adipocytes (not cell membranes or viral envelopes)

palmitic acid

a free fatty acid synthesized by cells

sphingomyelin

a phospholipid with a sphingoside backbone (instead of a glycerol backbone)

chargraff's rules

1. A=T and G=C 2. G + A = C + T

order in which the precursors of steroid hormones are synthesized (cholesterol synthesis)

isoprene --> monoterpene --> squalene --> cholesterol --> steriod hormones

how many isoprene units are in monoterpene

two

how many isoprene units are in triterpene (ex: squalene)

six

what moves the slowest in an agarose gel during electrophoresis

molecules with largest molecular weight

what nucleotide has the greatest molecular weight

guanosine

what is the function of sphingolipids

structural lipids (provide structue to cell membrane)

what type of fatty acid chain provides the greatest flexibility in membranes

short unsaturated fatty acids

what factors would cause the fastest time for DNA to reanneal (3)

short strands, ~physiological pH, highest salt concentration

lipid raft

regions of relatively high order of the cell membrane (have high cholesterol content)

what functional group is abundant in waxes

esters

dexyribose structure

ribose structure

how many hydrogen bond acceptors and donors does thymine or uracil have

1 donor and 1 acceptor

how many hydrogen bond acceptors and donors does adenine have

1 donor and 1 acceptor

how many hydrogen bond acceptors and donors does cytosine have

1 donor and 2 acceptors

how many hydrogen bond acceptors and donors does guanine have

2 donors and 1 acceptors

is ribose a pyranose or furanose

furanose

what is the relationship between D-mannose and D-glucose

epimers

is sucrose a reducing sugar

no (it does not have a free anomeric carbon)

is lactose a reducing sugar

yes (it has a free anomeric carbon)

which type of double bond in a fatty acid most increases fluidity

cis bond

by which properties could phospholipids in the cell membrane be separated (3)

charge, mass, and solubility

differences in structure between sphingophospholipids and glycerophospholipids

glycerophosplolipids have a glycerol head with 2 fatty acid tails, sphingophospholipids have a sphingosine head and one fatty acid tail

hydrolyzable lipids (4)

triaglycerols, emulsifying agents, sphingolipids, waxes

nonhydrolyzable lipids (3)

steroids, prostaglandins, fat-soluble vitamins

how can all lipids be processed in digestion

all lipids can be emulsified

what is the benefit of forming micelles

increases surface area of lipids available for hydrolysis by lipases

fat-soluble vitamins (4)

vitamins A, D, E, and K

what is the mechanism by which DNA polymerase adds a dNTP to a growing DNA strand

the hydroxyl group at the 3' end of the strand attacks the 5' a-phosphate of the dNTP

what is the structure in phospholipids that prevents simple diffusion of hydophilic molecules

H3C-(CH2)14-R1

what does the Tollen's test detect

reducing sugars

major role of triacylglycerols

storage lipids

cholesterol structure

what is the product of deamination of cytosine

uracil

what is the result of esterification cholesterol

moves the cholesterol from the lipid particle surface to the core (bc it is much less polar)

what does centrifugation separate molecules by

density

what does precipitation separate molecules by

reactivity

what is the stereochemical configuration of most sugars in the body

D- enantiomer

how to determine stereochemical configuration of a sugar

if the highest number stereocenter is R, the sugar is D; if it is S, the sugar is L

what functional groups are found in galactose (3)

primary alcohol, secondary alcohol, aldehyde

at which carbon does a glycosidic bond form

C1 (anomeric carbon)

in what direction do exonucleases act

3' --> 5' (opposite of DNA synthesis)

what type of fatty acids are increased by cells at low temps

unsaturated (have pi bond)

what is the total number of anomeric carbons in disaccharides linked by B-glycosidic bonds

2 (all disaccharides have 2 regardless of configuration)

how to identify the anomeric carbon in a disaccharide

carbon that has 2 bonds with oxygen

glucosidase function

breaks glycosidic bonds, resulting in greater sweetness

why do animal cells store glucose as glycogen

a glycogen molecule composed of 1,000 glucose units exerts less osmotic pressure than 1,000 free glucose monomers