Biochem test 2 Flashcards
(173 cards)
1
Q
carbohydrate
A
carbon-based molecules rich in hydroxyl groups
2
Q
monosaccharides
A
aldehydes or ketones that contain two or more hydroxyl groups
- fuel and fundamental constituent of living systems
- can be linked together to form a variety of oligosaccharide structures
- smallest monosaccharides are composed of 3 carbons
3
Q
smallest monosaccharides
A
- dihydroxyacetone
- D-Glyceraldehyde
- L-Glyceraldehyde
4
Q
isomer
A
same molecular formula, different structures
5
Q
constitutional isomers
A
differ in the attachment of atoms
6
Q
stereoisomers
A
atoms are connected in the same order but differ in spatial arrangement
7
Q
enantiomers
A
nonsuperimposable mirror images
8
Q
diastereomers
A
isomers that are not mirror images
9
Q
anomers
A
isomers that differ at a new asymmetric carbon atom found on ring closure
10
Q
epimers
A
differ at one of several asymmetric carbon atoms
11
Q
most vertebrate monosaccharides have what configuration
A
D
12
Q
basis for ring formation
A
- reaction of aldehyde with alcohol to form a hemiacetal or a ketone with an alcohol to form a hemiketal
13
Q
ketose fructose structure
A
- intramolecular hemiketal
- 5 carbon ring (furanose)
13
Q
glucose structure
A
- intramolecular hemiacetal
- 6 carbon ring (pyranose)
14
Q
anomer
A
formed through formation of a cyclic hemiacetal which makes another diastereoisomeric form
15
Q
alpha form
A
hydroxyl at C-1 is below the plane of the ring
16
Q
beta form
A
hydroxyl at C-1 is above the plane of the ring
17
Q
pyranose ring conformations
A
boat and chair conformation
18
Q
chair form
A
substituents on carbon ring can be axial and equatorial
19
Q
axial
A
nearly parallel
- sterically hinder each other if on same side of the ring
20
Q
equatorial
A
nearly perpendicular to plane
- less crowded
21
Q
furanose ring conformations
A
- not planar
- commonly adopt envelope form
22
Q
reducing sugar
A
reacts with oxidizing agents
- glucose is a reducing sugar
23
Q
hemoglobin A1c
A
determining amount of this in blood allows one to monitor the long-term control of blood glucose levels in diabetes
24
a solution of glucose contains...
1/3 alpha anomer and 2/3 beta anomer, and 1% open chain
- two forms are in equilibrium
24
glucose as a reducing sugar
- can react with amino groups, Lys and Arg residues in proteins
25
Advanced glycation end products (AGEs)
- reactions between carbohydrates and proteins often impair protein function
- implicated in number of pathological conditions
26
O-glycosidic bond
bond formed between anomeric carbon atom and an oxygen atom of an alcohol
27
N-glycosidic bond
bond formed between anomeric carbon atom and an amine
28
phosphorylation
- common modification of carbohydrates
- makes sugars anionic and prevents them from leaving the cell
- also facilitates the metabolism of sugars
29
oligosacccharides
containing two or more monosaccharides linked by O-glycosidic bonds
30
sucrose
- composed of a glucose linked to a fructose
- alpha linkage for glucose and beta for fructose
- cleaved by sucrase (invertase)
31
lactose
disaccharide of milk
- consists of a galactose linked to a glucose by a beta-1,4 linkage
- cleaved by lactase
32
maltose
- degradation product of large oligosaccharides
- composed of two glucose molecules linked by alpha-1,4 linkage
- hydrolyzed by maltase
33
storage of glucose
free glucose cannot be stored because in high concentrations glucose will disturb the osmotic balance of the cell
- needs to be stored as a large polymer
34
glycogen
- polysaccharide
- glucose storage form
35
how are glucose units in glycogen linked
alpha-1,4-glycosidic bonds with branches formed by alpha-1,6-glycosidic bonds about every 12 glucose units
36
how is glucose stored in plants
-stored as starch
37
two forms of starch
amylose and amylopectin
38
amylose
linear polymer of glucose units linked by alpha-1,4-glycosidic bonds
- unbranched
39
amylopectin
- branched polymer
- alpha-1,6-glycosidic bond for every 30 alpha-1,4-glycosidic bonds
40
cellulose
- structural component of plants
- made of chains of glucose\- homopolymer of glucose units linked by a beta-1,4-glycosidic bond
41
beta linkage
yields a straight chain capable of interacting with other cellulose molecules via H-bonds to form strong fibrils
42
alpha linkage
form compact hollow cylinders suitable for accessible storage
43
cellulose in mammals
- mammals cannot digest cellulose
- useful in diet
- increase rate at which digestion products pass through the large intestine (inc rate = minimize exposure to toxins in diet)
44
soluble fibers
- ex: polygalacturonic acid (pectin)
- aid in digestion
- facilitate absorption of nutrients in diet
45
human milk oligosaccharides
- more than 150 oligosaccharides in human milk (composition and amount vary among women)
- not digested by infant, protect against bacterial infection
- prevent growth of certain Streptococcus bacteria which may be transferred from mothers vaginal epithelium and cause pneumonia, blood poisoning, or meningitis in the infant
- milk has IgM, IgE, IgD, IgG and IgA
46
glycoproteins
formed when carbohydrates are linked to proteins
47
glycoproteins
- mostly protein by weight
- variety of roles, including as membrane proteins
48
proteoglycans
- attached to a particular polysaccharide called a glycosaminoglycan
- mainly carbohydrate by weight
- plays structural roles or act as lubricants
49
mucins/mucoproteins
- protein in characteristically attached to the carbohydrate by N-acetylgalactosamine
- mainly carbohydrate by weight
- often act as lubricants
50
N-linkage vs O-linkage
in glycoprotein, carbohydrate is attached to the nitrogen atom in the side chain of asparagine (N-linkage) or to the oxygen atom of the side chain of serine or threonine (O-linkage)
51
N-linked polysaccharides
have a common pentasaccharide core, consisting of 3 mannoses and 2 N-acetylglucosamine units
52
erythropoietin
- glycoprotein
- 40% carbohydrate by weight
- secreted into blood by kidneys to stimulate the production of red blood cells
- glycosylation of erythropoietin enhances the stability of the protein in the blood
53
N-acetylglucosamine modification
- attached to serine or threonine residues by GlcNAc transferase when nutrients are abundant
- attachment is reversible with GlcNAcase removing the carbohydrate
- improper regulation of the transferase has been linked to pathological conditions (insulin resistance, diabetes, cancer, neurological pathologies)
54
proteoglycans
proteins attached to glycosaminoglycans, which make up as much as 95% of the proteoglycan by weight
- key components of the extracellular matrix and serve as lubricants
55
glycosaminoglycans
composed of repeating units of a disaccharide, one of which is a derivative of an amino sugar and one of which carries a negative charge as either a carboxylate or sulfate
56
mucopolysaccharidoses
- Hurler disease
- pathological conditions that result from the inability to degrade proteoglycans
- all result in skeletal deformities and reduced life expectancies
57
Hurler disease
- S/S: mucopolysaccharidosis, depressed nasal bridge, thick lips and earlobes, irregular teeth
- glycosaminoglycans cannot be degraded
- increase in soft tissue of facial regions
58
cartilage
- composed in part of the proteoglycan aggrecan as well as the protein collagen
- glycosaminoglycan component of aggrecan cushions joints by releasing water on impact and then rebinding water
(collagen provides structure/tensile strength, aggrecan serves as shock absorber)
59
Chitin
a glycosaminoglycan found in exoskeleton of insects, crustaceans, and arachnids
60
mucins
- protein component is extensively glycosylated to serine and threonine residues with the first carbohydrate being N-acetylgalactisamine
- serve as lubricants and adhere to epithelial cells, acting as protective barrier
- overproduced in conditions such as bronchitis and cystic fibrosis and in adenocarcinomas (cancers of the glandular cells of epithelial origin)
61
variable number of tandem repeats
region of protein backbone rich in serine and threonine
- site of glycosylation
62
protein glycosylation
| where does it occur
- takes place in the lumen of the endoplasmic reticulum and in the golgi apparatus
63
N-linked glycosylation
| where does it occur
begins in endoplasmic reticulum and continues in the golgi complex
64
O-linked glycosylation
| where does ot occur
- occurs only in Golgi complex (sorting center for proteins of various fates)
65
dolichol phosphate
- isoprene derivative
- carries large oligosaccharides destined for attachment to asparagine
66
glycosyltrannsferases
catalyze the formation of glycosidic bonds
- monosaccharide substrates for glycosyltransferases are activated by attachment to uridine diphosphate (UDP)
67
blood groups
- all blood groups share oligosaccharide foundation called O
- A form created if N-acetylgalactosamine is added to O by specific glycosyltransferase, while B form is created if galactose is added by another transferase
- O= lack both enzymes
- AB= expresses both enzymes
- either A or B = express one enzyme
68
I cell disease
- autosomal recessive
- inherited lysomal storage disorder
- Defect: N-acetylglucosaminyl-1-phosphotransferase leads to failure of Golgi to phosphorylate mannose residues
- S/S: gingival hyperplasia, restricted joint movements, claw hand deformities, Kyphoscoliosis
69
glycan-binding proteins
bind to specific oligosaccharides on cell surface
70
lactins
particular class of glycan-binding proteins
- promote interactions between cells and within cells
- lectins on one cell recognize and bind to carbohydrates on another cell with multiple weak interactions
- binding facilitates cell-cell interaction (important for processes such as building tissue and facilitating transmission of information)
71
C-type lectins
- calcium ion facilitates interaction between the protein and the carbohydrate
72
selectins
members of the C-type family
- bind immune-system cells to sites of injury in the inflammatory response
73
L-selectin
- allowing attachment of an embryo to the mothers uterus
74
L-lectins
chaperones (assistants in protein folding) in eukaryotic endoplasmic reticulum, while some other have been found to be potent insecticides
75
how do pathogens gain entry into cells
binding to carbohydrates on cell surface
76
influenza virus
recognizes sialic acid residues linked to galactose residues that are present on cell-surface glycoproteins, the viral protein that binds to these sugars is a lectin called hemagglutinin
- infection spreads when a viral protein, neuraminidase (sialidase) cleaves the glycosidic bonds between the sialic acid residues and the rest of the cellular glycoprotein, freeing the virus to infect new cells
- antiflu agents are neuraminidase inhibitors
77
plasmodium falciparum
parasitic protozoan that causes malaria also relies on glycan binding to infect and colonize its host
78
endocytosis
getting into cell
78
alpha-glucosidase inhibitors
(maltase inhibitors)
- help maintain blood glucose homeostasis
- essential because hyperglycemia can lead to advanced glycation product and type 1 diabetes(absent insulin) or type 2 diabetes (ineffective insulin)
78
exocytosis
leaving cell, infects more cells
79
digestion of glycogen
- degradation into smaller oligosaccharides by alpha-amylase (secretes by the salivary glands and pancreas)
- further digested by alpha-glucosidase
- two competitive inhibitors or this enzyme are acarbose and miglitol, either can be administered at the start of a meal to reduce post-meal glucose absorption in type 2 diabetes
80
common types of membrane lipids
- phospholipids
- glycolipids
- cholesterol
81
lipids
water insoluble biomolecules that are highly soluble in organic solvents
- serve as fuel molecules, energy stores, signal molecules/messengers, membrane components
82
phospholipid components
one or two fatty acid tails, a platform, a phosphate, and an alcohol
83
common platforms
glycerol and sphingosine
84
phosphoglyycerides/ phosphoglycerols
phospholipids with a glycerol platform
- formed when an alcohol is added on to phosphatidate
- derived from phosphatidate by the formation of an ester bonds between the phosphate and an alcohol
85
sphingomyelin
common membrane lipid in which the primary hydroxyl group of sphingosine is esterified to phosphorylcholine
86
glycolipids
| derived from
carbohydrate containinng lipids derived from sphingosine
- carbohydrate is linked to the primary alcohol of sphingosine
87
cerebrosines
simplest glycolipids, containing only a single sugar (glucose or galactose)
88
gangliosides
contain a branched chain of as many as seven sugar molecules
89
where is carbohydrate component of glycolipids located
one the extracellular surface of the cell membrane where they play a role in cell-cell recognition
90
cholesterol
- steroid that is modified on one end by the attachment of a fatty acid chain and at the other end by a hydroxyl group
- in membranes, the hydroxyl group interacts wuth phospholipid head groups
91
membrane lipids
- amphipathic molecules containing hydrophobic and hydrophilic properties
- fatty acid tail = hydrophobic properties
- alcohol and phosphate group (polar head group) = hydrophilic properties
- polar head favors contact with water, hydrocarbon tail interact with one another instead of with water
92
membrane lipids vs membrane proteins
- membrane lipids = establish a permeability barrier to polar molecules and ions
- membrane proteins = allow transport of molecules and information across the membrane
- membranes vary in protein content from less than 20%-75%
- membrane proteins can be visualized by SDS-PAGE
93
Schwann cell
- insulates axon
- relatively low membrane protein content
- plasma membrane is lipid rich, lipid serves as insulator, allowing rapid transmission of nerve impulses
- wrapping of this type of cell around an axon is called myelination
- multiple sclerosis= demyelination disease, impairing myelin assembly or damaging existing myelin
94
MS
autoimmune inflammation
- more common in females (20-30 years old)
- decreased Vitamin D
- demyelination of CNS with subsequent axonal damage
- S/S = painful unilateral vision loss, speech, spinal cord syndrome--> inc with inc body temp (hot bath, exercise... etc.)
95
Guillian-Barre Syndrome
destroys Schwann cell via inflammation and demyelination of intron fibers, sensory fibers, and peripheral nerves (CV III- XII)
- ascending paralysis
- autoimmune
96
integral membrane proteins
embedded in hydrocarbon core of the membrane
97
peripheral membrane proteins
bound to the polar head groups of membrane lipids or to the exposed surfaces of integral membrane proteins
98
common structural feature of integral membrane proteins
membrane-spanning alpha helices
99
bacteriorhodopsin
light-powered proton pump
- integral membrane protein composed of seven membrane spanning helices
100
beta strands
can be composing integral membrane proteins that form a pore in the membrane
101
porin
bacterial protein that is an example of a beta strand-rich integral membrane protein
- outside surface that interacts with the hydrophobic interior of the membrane is composed of hydrophobic amino acids (inside is polar and filled with water)
102
prostaglandin H2 synthase-1
portion embedded in membrane
- promotes inflammatory response
103
cyclooxygenase (COX) activity
dependent on channel connecting the active site to the membrane interior
104
asprin
inhibits cyclooxygenase activity by obstructing the channel
- pain relief/fever reduction
- transfers an acetyl group to a serine residue in prostaglandin H2 synthase-1
105
hydrophobic protein membrane associations
done by attaching one of a variety of possible hydrophobic groups
106
transmembrane helices
- can be accurately predicted from amino acid sequences
- an alpha helix of 20 residues can traverase a lipid bilayer
- hydrophilicity of each amino acid can be quantified by determining the free energy required to transfer the amino acid from a hydrophobic environment
107
window
stretch of 20 amino acids
- used to examine a protein sequence
- free energy of transferring each stretch of 20 amino acids from a hydrophobic to a hydrophilic environment
108
hydropathy plot
free energy plotted against the first amino acid of the window
- can identify potential membrane-spanning helices when sequence but little additional information is known for a protein
109
gram positive
bacteria and archaea enclosed bya single membrane surrounded by a thick cell wall
110
gram negative
bacteria surrounded by 2 membranes, with a cell wall (made of proteins, peptides, and carbohydrates) lying between them
111
periplasm
space between two membranes in gram negative bacteria
112
gram staining of bacteria
gram positive retain crystal violet stain in their thick cell walls, gram negative bacteria have a thinner cell wall that does not retain the stain well
113
eukaryotic cells
- do not have cell walls
- curroundedd by single membrane (plasma membrane/cell membrane)
- have membranes inside the cell that allow compartmentalization of function
114
receptor mediated endocytosis
how cells aquire molecules from theis environment
- ex: internalization of iron-bound transferrin in association with thetransferrin receptor
115
clathrin
protein that helps to internalize receptors bound to their cargo
116
how are molecules released from cell
fusion of internal membranes with the plasma membrane
117
SNARE
facilitate membrane fusion by forming tightly coiled four-helical bundles
118
cardiolipin
| structure
(diphosphatidylglycerol)
- unusual structure compared with other phosphoglycerides
- net charge of -2 and inverted cone shape
- most often in membranes of bacteria/archaea/ inner membrane of mitochondria
119
cardiolipin in mitochondria
involved in the structure and function of the respirasome which is essential in ATP synthesis
120
tafazzin
- necessary to proper synthesis and maintenance of cardiolipin levels
- catalyzes the transfer of linoleate chains from phosphatidylcholine to immature cardiolipin
121
Barth syndrome
results from mutations that reduce the catalytic activity of tafazzin
- symptoms: dilation of the heart chambers. exercise intolerance, and impaired growth
- malformed mitochondria and distorted inner membranes and pooly functioning respirasomes due to improper assembly of the protein complexes
122
glycolysis
1 molecule of glucose -> 2 molecules pyruvate and net production of 2 molecules of ATP
- anaerobic (does not require oxygen)--> evolved before oxygen was abundant in the atmosphere
- produces pyruvate which has various fates depending on the organism and whether oxygen is abundant
123
pancreatic and salivary alpha-amylase
cleave the alpha-1,4-bonds of starch and glycogen to yield maltose and maltotriose
124
alpha-glucosidase
(maltase)
- completes the digestion od these di and trisaccharides into glucose
125
dextrin
dextran-rich in alpha-1,6-bonds
-alpha-Dextrinase degrades the limit dextrin
126
sucrase
hydrolyzes sucrose
127
lactase
cleaves lactose
128
glucose
- almost all organisms use glucose as fuel
- in mammals, glucose is the only fuel the brain uses under nonstarvation conditions and the only fuel red blood cells are able to use at all
129
why is glucose such a prominent fuel in life forms
1) glucose may have been available for primitive biochemical systems because it can form under prebiotic conditions
2) glucose is the most stable hexose
3) glucose has a low tendency to nonenzymatically glycosylate proteins
130
glycolysis in eukaryotic cells
glycolytic enzymes are organized in cytoplasmic supramolecular complexes
- efficient due to substrate channeling between active sites and prevents the release of toxic intermediates
131
two stages of glycolysis
Stage 1: traps glucose in the cell and modifies it so that it can be cleaved into a pair of phosphorylated 3-carbon compounds
Stage 2: oxidizes the 3-carbon compounds to pyruvate while generating two molecules of ATP
132
after entering cell glucose is...
phosphorylated at the expense of ATP to form glucose 6-phosphate
133
hexokinase
- requires Mg2+ or Mn2+ as a cofactor
- catalyzes reaction from glucose to glucose 6-phosphate
- uses substrate-binding induced fit to help exclude water and minimize undesired hydrolysis of ATP
134
kinase
enzyme that catalyzes the transfer of a phosphoryl group from ATP to a variety of 6-carbon sugars (hexoses)
135
phosphoglucose isomerase
catalyzes the conversion of glucose 6-phosphate to fructose 6-phosphate
- reaction is REVERSIBLE
136
phosphfructokinase-1
catalyzes reaction from fructose 6-phosphate to fructose 1,6-bisphosphate by the addition of a second phosphate
- IRREVERSIBLE reaction
137
how does first stage of glycolysis end
- cleavage of fructose 1,6-bisphosphate into dihydroxyacetone phosphate and gyceraldehyde 3-phosphate
- REVERSIBLE reaction
- Glyceraldehyde 3-phosphate can be processed to pyruvate to yield ATP, dihydroxyacetone phosphate cannot
138
aldose
catalyzes reaction of fructose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate
139
triose phosphate isomerase
interconverts glyceraldehyde 3-phosphate and dihydroxyacetone phosphate--> so dihydroxyacetone phosphate can be metabolized
- only glycolytic enzyme for which genetic deficiency in expression can be lethal
140
mechanism: tris=ose phosphate isomerase salvages a 3-carbon fragment
- converts dihydroxyacetone phosphate into glyceraldehyde 3- phosphate
1) glutamate 165 acts as a general base catalyst and removes a proton from C-1 of the substrate to form the enediol intermediate
2) Glutamate 165, now acting as a general acid catalyst donates a proton to C-2 while histidine 95 removes a proton from C-1
3) product is formed and glutamate 165 and histidine 95 return to their initial states
141
design of triose phosphate isomerase
- considered to be a kinetically perfect enzyme because its rate of catalysis is near the diffusion limit
- the enediol intermediiate may potentially decompose into the very reactive methyl glyoxal(structural features in enzyme prevent production of this undesired product)
142
second stage of glycolysis begins with...
a compound with high phosphoryl-transfer potential, 1,3-bisphosphoglycerate is generated by the oxidation of glyceraldehyde 3-phosphate in a reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase
143
glyceraldehyde 3-phosphate dehydrogenase
catalyzes oxidation of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate
144
two steps of glyceraldehyde 1,3-bisphosphate
1) oxidation of carbon 1 in glyceraldehyde 3-phosphate to an acid
2)formation of glyceraldehyde 1,3-bisphosphate from acid
- linked by the formation of a thioester in active site of glyceraldehyde 3-phosphate dehydrogenase
145
meachnism of oxidation of glyceraldehyde 3-phosphate by thioester intermediate
1) glyceraldehyde 3-phosphate reacts with a cysteine residue to form hemithioacetal
2) thioester is formed by the transfer of a hydride to NAD+
3) NADH is exchanged for NAD+ (the charge on NAD+ facilitates the attack by the phosphate on the thioester)
4) phosphate attacks the thioester, forming 1,3-bisphosphoglycerate
146
phosphoglycerate kinase
-catalyzes reaction of 1,3-bisphosphoglycerate to 3-phosphoglycerate
- generates ATP by substrate-level phosphorylation
- also catalyzes reaction of 3-Phosphoglycerate to 2-phosphoglycerate
147
enolase
converts 2-phosphoglycerate into phosphoenolpyruvate in a dehydration reaction
148
pyruvate kinase
catalyzes reaction of phosphoenolpyruvate into pyruvate
- generates 2 "profit" ATP
149
phosphoglycerate mutase
uses a phosphorylates enzyme intermediate and substrate passes through 2,3-bisphosphorylated form
150
net reaction of glucose into pyruvate
Glucose + 2 Pi + 2 ADP + 2 NAD+ --> 2 pyruvate +2 ATP +2 NADH + 2H+ + 2H2O
151
NAD+ regeneration
- cells have limited amounts of NAD+ which is derived from niacin (vitamin B3)
- NAD+ can be regenerated by further oxidation of pyruvate to CO2 or by the formation of ethanol of lactate from pyruvate
- glucose to pyruvate generates ATP but for ATP synthesis to continue, NADH must be reoxidized to NAD+
152
3 possible fates of pyruvate
fermentation (two types) or metabolism in citric acid cycle and electron transport chain
153
fermentations
ATP generating pathways in which electrons are removed from one organic compound and passed to another organic compound
154
alcoholic fermentation
regeneration of NAD+ by processing pyruvate to ethanol
155
lactic acid fermentation
pyruvate is reduced to lactate to regenerate NAD+
156
net reaction of lactic acid fermentation
Glucose + 2Pi + 2 ADP --> 2 lactate + 2 ATP + 2 H2O
157
third fate of pyruvate
- completely oxidize the pyruvate through pyruvate processing (to generate acetyl CoA) and the citric acid cycle (to oxidize the acetyl group)
- electrons are transferred to the final acceptor in the electron transport chain via aerobic metabolism (as electrons are delivered from NADH to the electron transport chain, NAD+ is restored)
158
aerobic metabolism through citric acid cycle and electron transport chain equation
Pyruvate + NAD+ + CoA --> acetyl CoA + CO2 + NADH + H+
159
fermentations provide usable energy...
in the absence of oxygen
- obligate anaerobes cannot survive in the presence of O2
- more fermentations than just alcoholic and lactic acid fermentation
160
fructose
- fructose: from table sugar or high fructose corn syrup
- galactose: from milk sugar
- can be converted into glycolytic intermediates
- in liver, fructose is metabolized by the fructose 1-phosphate pathway
- in other tissues, fructose is directly phophorylated by hexokinase
161
excessive fructose consumption
- commonly used sweetener
- excess consumption of fructose has been linked to fatty liver, insulin insensitivity, obesity, and type 2 diabetes
- in liver, frucotse metabolism bypasses the key regulatory enzyme phosphofructokinase
- excess pyruvate is converted into acetyl CoA and then into fatty acids
162
glucose converted into...
glucose 6-phosphate by galactose-glucose interconversion pathway, which begins with the phosphorylation of galactose by galactokinase
163
sum of reactions of the galactose-glucose conversion pathway
Galactose + ATP--> glucose-1-phosphate + ADP + H+
164
phosphoglucomutase
converts glucose 1-phosphate to glucose 6-phosphate
165
lactose intolerance
(hypolactasia)
- occurs because most adults lack lactase (enzyme that degrades lactose)
- Northern Europeans have a mutation that prevents the decline of lactase activity after weaning
- in lactase-deficient individuals, gut bacteria ferment lactose to lactic acid (generates methane (CH4) and hydrogen gas(H2)--> causes discomfort and disrupts water balance in intestine)
166
galactose is highly toxic if...
transferase is missing
167
galactosemia
results if galactose 1-phosphate uridyl transferase activity is deficient
- Symptoms: failure to thrive, jaundice, and liver enlargement that can lead to cirrhosis, cataract formation may also occur
- most common treatment is to remove galactose (and lactose) from the diet
168
cataracts
- clouding of the lens
- form because galactose is converted into galactitol which is poorly metabolized and accumulates in the lens
- water diffuses into the lens to maintain osmotic balance, causing cataract formation
169
enzymes that catalyze irreversible reactions
1) hexokinase
2) phosphofructokinase
3) pyruvate kinase
