Block B Part 2: Carbohydrates, Lipids and Cholesterol Flashcards
What are 3 uses of carbohydrates?
Answers include:
Coating of cell surfaces
Modification of secreted proteins
Part of receptors for a variety of pathogens
Form basis of human blood groups
Allow tremendous structural diversity
(Lecture 3, Slide 4)
What are the names of 3,4,5,6 and 7 carbon monosaccharides?
Trioses
Tetroses
Pentoses
Hexoses
Heptoses
(Lecture 3, Slide 5)
What is the general formula that most sugars conform to?
(CH2O)n where n is between 3 and 7
(Lecture 3, Slide 6)
What are the 2 groups that sugars contain 1of?
An aldehyde or a ketone group
(Lecture 3, Slide 6)
What makes sugars reactive?
Carbon-oxygen double bonds
(Lecture 3, Slide 6)
What are monosaccharides?
The smallest type of sugars (trioses)
(Lecture 3, Slide 7)
What are the 2 forms of glucose?
Ring-form and open chain form
(Lecture 3, Slide 9)
What form of glucose is favoured at equilibrium?
The ring form, with less than 0.1% of molecules in open chain form
(Lecture 3, Slide 9)
Why is glucose primarily found in the ring form at equilibrium?
As it’s energetically more stable
(Lecture 3, Slide 10)
How are sugar alcohols formed?
The reduction of the aldehyde group (R−CH=O) to a hydroxyl group (-OH)
(Lecture 3, Slide 12)
What 2 things are monosaccharides joined to alcohols, amines and phosphates useful for?
Signal molecules
Facilitate metabolism
(Lecture 3, Slide 13)
What is an O-glycosidic bond?
A chemical bond between an oxygen atom and a carbon atom that connects a monosaccharide to another monosaccharide, an alcohol or a protein
(Lecture 3, Slide 13)
What is an N-glycosidic bond?
A chemical bond between a nitrogen atom and a carbon atom that connects a monosaccharide to a nitrogenous base or the amino acid lysine in a protein
(Lecture 3, Slide 13)
What occurs in a phosphorylation reaction to a monosaccharide?
A phosphoryl group (a phosphorus atom bonded to 3 oxygen atoms) is added to the monosaccharide
(Lecture 3, Slide 14)
What 3 things does phosphorylation of a monosaccharide do?
Makes thesugar anionic (a substance that possess a negative charge)
Traps the sugar within a cell
Creates a reactive intermediate of sugar metabolism
(Lecture 3, Slide 14)
What 3 things are classified as sugars?
Monosaccharides
Disaccharides
Oligosaccharides
(Lecture 3, Slide 17)
What 2 things are classified as polysaccharides?
Starches
Non-starch polysaccharides
(Lecture 3, Slide 17)
How are disaccharides formed?
By condensation between 2 monosaccharides, forming an O-glycosidic bond
(Lecture 3, Slide 18)
How many monosaccharides are in an oligosaccharide?
3 - 10
(Lecture 3, Slide 18)
Are oligosaccharides digested by the body?
Generally not
(Lecture 3, Slide 18)
What are intrinsic sugars?
Sugars contained within plant cell walls
(Lecture 3, Slide 18)
What are extrinsic sugars?
Sugars that are free in solution (such as dental plaque, caries)
(Lecture 3, Slide 18)
Are intrinsic and extrinsic sugars good or bad for the body?
Intrinsic sugars are good for the body whereas extrinsic sugars are bad for the body
(Lecture 3, Slide 18)
What sugar is an exception to extrinsic sugars being bad?
Lactose being a desirable extrinsic sugar from milk
(Lecture 3, Slide 18)
What are 3 simple sugars?
Answers Include:
Sucrose
Fructose
Glucose
Galactose
Maltose
Lactose
Mannose
(Lecture 3, Slide 19)
What are the 3 most common disaccharides?
Sucrose
Lactose
Maltose
(Lecture 3, Slide 19)
What monosaccharides are in sucrose?
1 glucose and 1 fructose
(Lecture 3, Slide 19)
What monosaccharides are in lactose?
1 glucose and 1 galactose
(Lecture 3, Slide 19)
What monosaccharides are in maltose?
2 glucose monosaccharides
(Lecture 3, Slide 19)
What is the formula of sucrose, lactose and maltose?
C12H22O11
(Lecture 3, Slide 19)
What 2 places can we get sucrose from naturally?
Sugar cane or sugar beet
(Lecture 3, Slide 21)
Where is maltose originally isolated from?
Malt
(Lecture 3, Slide 22)
How is maltose produced?
In germinating cereals in the brewing process
(Lecture 3, Slide 23)
How is “malting” barley done?
Through maltose-producing amylases
(Lecture 3, Slide 23)
What does mashing permit in barley?
The amylases to convert the cereal’s starches into maltose
(Lecture 3, Slide 23)
What 2 things are produced when yeast ferments maltose?
Ethanol and carbon dioxide
(Lecture 3, Slide 23)
How are the carbons in ring forms of sugars numbered?
Moving clockwise from the top right oxygen atom
(Lecture 3, Slide 25)
What is starch?
A large molecule with a variable amount of glucose units, a storage carbohydrate of plants
(Lecture 3, Slide 27)
Is starch osmotically active?
No
(Lecture 3, Slide 27)
What 2 polysaccharides are components of starch?
Amylose and amylopectin
(Lecture 3, Slide 27)
What type of glycosidic bonds do starch and glycogen have?
α-1,4 glycosidic linkages
(Lecture 3, Slide 27)
How often does glucose branch to other glucose residues in amylopectin?
Every 30th glucose molecule
(Lecture 3, Slide 27)
How is glycogen different from amylopectin?
Glucose branches to other glucose residues every 10th glucose molecule in glycogen, as opposed to every 30th in amylopectin
(Lecture 3, Slide 27)
Can our bodies digest non-starch polysaccharides?
No
(Lecture 3, Slide 27)
State 1 example of a non-starch polysaccharide.
Cellulose , chitin or pectin
(Lecture 3, Slide 27)
What type of glycosidic bond does cellulose have?
ß-1,4 glycosidic linkages
(Lecture 3, Slide 27)
Why is uncooked starch resistant to digestion?
As it’s present as small insoluble molecules
(Lecture 3, Slide 28)
Why does cooking starch remove it’s resistance to digestion?
As cooking swells the granules
(Lecture 3, Slide 28)
What level does lactose activity drop to compared to the level it is at birth (%age)?
5 - 10% of level at birth
(Lecture 3, Slide 30)
Why is the decrease in lactose activity compared to birth level not as pronounced in northern Europeans?
As they are adapted to milk-producing domesticated animals
(Lecture 3, Slide 30)
What is lactose used as an energy source for?
Microorganisms in the colon
(Lecture 3, Slide 30)
What does lactose ferment to and what 2 things are also produced?
Ferments to lactate with methane and hydrogen gas also being produced
(Lecture 3, Slide 30)
Why does flatulence and diarrhea draw water into the intetine?
As lactate is osmotically active
(Lecture 3, Slide 30)
What is glycogen?
A readily mobilised storage form of glucose
(Lecture 3, Slide 34)
Why is glycogen not as energy-rich as fatty acids?
It is less reduced
(Lecture 3, Slide 34)
What does the controlled release of glucose from glycogen maintain?
Blood glucose level
(Lecture 3, Slide 34)
What 2 places are glycogen mainly stored?
The liver and skeletal muscle
(Lecture 3, Slide 34)
In liver hepatocytes (cells) what percentage of the fresh weight can glycogen make up?
8-10%
(Lecture 3, Slide 34)
How much percent of muscle mass can be glycogen?
1-2%
(Lecture 3, Slide 34)
Why does the uterus store glycogen during pregnancy?
To nourish the embryo
(Lecture 3, Slide 34)
How do polysaccharides have directionality?
As they have a reducing and a non-reducing end
(Lecture 3, Slide 36)
What is an acetal?
A molecule with 2 single bonded oxygens attached to the same carbon atom
(Lecture 3, Slide 28)
Why does glycogen not have a reducing end?
As it is not free but is covalently bonded to a protein named glycogenin as a beta-linkage to a surface tyrosine molecule
(Lecture 3, Slide 39)
What is glycogenin?
It’s a glycosyltransferase
(Lecture 3, Slide 39)
Is glycogenin a monomer, dimer or polymer?
Dimer
(Lecture 3, Slide 39)
Where does glycogenin sit in glycogen?
In the core
(Lecture 3, Slide 39)
What 2 things do glycogen granules contain?
Glycogen and the enzymes of glycogen synthesis and degradation
(Lecture 3, Slide 39)
What facilitates glycogen’s rapid synthesis and catabolism?
It’s many non-reducing ends
(Lecture 3, Slide 40)
What is the core structure of a phospholipid?
2 fatty acids connected to a glycerol molecule, with the glycerol also being connected to a phosphate, which is attached to an alcohol
(Lecture 4, Slide 4)
What are 3 major functions of cellular lipids?
P1 is a precursor of signalling molecules
P2 is a key signal in apoptosis
PC is a structural component of membranes
PE donates functional groups to membrane anchored proteins and has some structural roles and regulates curvature
(Lecture 4, Slide 6)
What is the difference between saturated and unsaturated fatty acids?
Saturated fatty acids have no double bonds whereas unsaturated fatty acids do
(Lecture 4, Slide 8)
What are 3 variations in fatty acyl (fatty acid) side chains in glycerophospholipids?
Carbon length (usually between 11 and 22 C)
Some GPLs exhibit enrichment of fatty acid content
Saturated vs unsaturated fatty acids
(Lecture 4, Slide 8)
What does enrichment of fatty acid content mean in the context of glycerophospholipids?
Deliberate modification of fatty acids in order to achieve a specific fatty acid profile
(Lecture 4, Slide 8)
What are 2 non-glycerol-lipids?
Sphingolipids and cholesterol
(Lecture 4, Slide 9)
What is an amphipathic molecule?
A molecule containing both hydrophilic and hydrophobic parts
(Lecture 4, Slide 10)
Which part of lipids are hydrophilic and hydrophobic?
Lipids have a hydrophobic tail and hydrophilic head
(Lecture 4, Slide 10)
Membranes are said to be “fluid” - what does this mean?
They accommodate protein conformational changes without loss of integrity
(Lecture 4, Slide 11)
What signalling molecule can lipids produce?
P1
(Lecture 4, Slide 12)
What can phosphorylate the inositol ring of a lipid?
Kinases
(Lecture 4, Slide 12)
What are the 2 products resulting from certain signals catalysing the breakdown of PtdIns(4,5)P2 (lipid with phosphorylated inositol ring)?
Inositol triphosphate and Diacylglycerol (DAG)
(Lecture 4, Slide 13)
What enzyme does glycerophospholipid (GPL) biosynthesis occur through?
Phosphatidate
(Lecture 4, Slide 15)
Where does glycerophospholipid GPL biosynthesis occur?
The endoplasmic reticulum
(Lecture 4, Slide 15)
How are phospholipids made from Phosphatidate?
An alcohol polar head group is added to the phosphate
(Lecture 4, Slide 15)
Why is phosphatidic acid phosphatase a key regulatory enzyme in lipid synthesis?
As when active, it can generate diacylglycerol (DAG)
(Lecture 4, Slide 16)
Why is generating diacylglycerol from phosphatidate important?
As it can activate with activated alcohols to form phospholipids it with fatty acyl CoA to form triacylglycerols
(Lecture 4, Slide 16)
What is phosphatidate converted into when phosphatidic acid phosphatase (PAP) is inactive and why?
CMP-DAG (Cytidine Monophosphate Diacylglycerol) for the synthesis of different phospholipids
(Lecture 4, Slide 16)
What is phosphatidylcholine (PC)?
A major component of lung surfactant, with it’s function being to maintain “surface tension” of fluid to keep alveoli “open”
(Lecture 4, Slide 18)
What happens when there are low levels of phosphatidylcholine (PC)?
Alveoli collapse
(Lecture 4, Slide 18)
What is respiratory distress syndrome?
It often affects premature babies and results in laboured breathing and blue fingers or toes
(Lecture 4, Slide 18)
How is respiratory distress syndrome treated?
With O2 ventilation and artificial surfactant
(Lecture 4, Slide 18)
What is the precursor for sphingomyelin?
Ceramide
(Lecture 4, Slide 19)
What are 2 functions of sphingomyelin?
It’s a major structural component of membranes and the source of messenger molecules
(Lecture 4, Slide 19)
How are sphingolipids further modified?
The addition of sugars
(Lecture 4, Slide 20)
What are gangliosides and what do they do?
They are a type of glycosphingolipid and are important cell surface molecules which are highly prevalent in nervous tissue
(Lecture 4, Slide 20)
What is Tay Sachs disease?
An inherited disorder where the body cannot degrade gangliosides, resulting in lysosomes becoming filled with them
(Lecture 4, Slide 21)
What is the treatment for Tay Sachs disease?
No treatment exists
(Lecture 4, Slide 21)
Is sphingosine present in all sphingolipids?
Yes, it is a key component of all sphingolipids
(Lecture 4, Slide 22)
Sphingosine is phosphorylated by ______ to generate _________, which is a key signalling molecule?
Sphingosine kinase, sphingosine 1-phosphate
(Lecture 4, Slide 22)
What is cholesterol?
Cholesterol is an essential component of membranes which helps maintain membrane bilayer integrity and regulate permeability
(Lecture 4, Slide 24)
What 3 things is cholesterol the precursor of?
Steroids, vitamins and bile salts
(Lecture 4, Slide 24)
What is excess cholesterol associated with?
Cardiovascular disease
(Lecture 4, Slide 24)
What happens in the first step of cholesterol biosynthesis?
Synthesis of isopentyl pyrophosphate via mevalonate
(Lecture 4, Slide 25)
What happens in the second step of cholesterol biosynthesis?
Condensation of 6 molecules isopentyl pyrophosphate to form squalene
(Lecture 4, Slide 25)
What happens in the third step of cholesterol biosynthesis?
Cyclisation of squalene and further processing to form cholesterol
(Lecture 4, Slide 25)
What does the rate of cholesterol depend on and how much does this vary?
Rate of cholesterol varies several hundred fold and depends on diet
(Lecture 4, Slide 31)
What type of synthesis does cholesterol experience?
Feedback regulation (rate of synthesis is dependant on how much cellular cholesterol is present)
(Lecture 4, Slide 31)
Where are 2 major sites of synthesis for cholesterol?
The liver and intestines
(Lecture 4, Slide 31)
What step does HMG-CoA reductase catalyse of cholesterol biosynthesis and how does this help regulate the biosynthesis?
It catalyses the committed step of cholesterol synthesis, therefore regulating cholesterol synthesis by its amount and activity
(Lecture 4, Slide 31)
What is the committed step of a metabolic pathway?
The slowest step
(Lecture 4, Slide 31)
What are the 4 ways in which HMG-CoA reductase regulates cholesterol biosynthesis?
- Rate of synthesis of HMG-CoA reductase mRNA
- Rate of translation of HMG-CoA reductase to protein
- Rate of degradation of HMG-CoA reductase protein
- Phosphorylation state of HMG-CoA reductase protein
(Lecture 4, Slide 32)
Why is the rate of HMG-CoA reductase mRNA controlled?
As HMG-CoA helps catalyse cholesterol biosynthesis
(Lecture 4, Slide 33)
How is HMG-CoA reductase mRNA controlled?
When cholesterol levels are low, sterol regulatory element binding protein transcription factor (SREBP)is activated and binds to the promoter region of the HMG-CoA reductase gene
When cholesterol levels are high, serine protease cleaves off SREBP in a 2 step process, decreasing production of HMG-CoA reductase
(Lecture 4, Slide 33)
How is the rate of translation of HMG-CoA reductase mRNA to a protein controlled?
Translation is inhibited by nonsterol metabolites derived from mevalonate
(Lecture 4, Slide 34)
What is the first step of HMG-CoA reductase protein being degraded?
HMG-CoA reductase membrane domain senses increasing levels of sterols then interacts with ubiquitinating enzymes.
(Lecture 4, Slide 34)
What is the second step of HMG-CoA reductase protein being degraded?
HMG-COA reductase becomes polyubiquitinated and is extracted from the membrane and then is degraded by the proteasome
(Lecture 4, Slide 34)
How does phosphorylation of HMG-CoA reductase stop cholesterol synthesis?
It decreases its catalytic activity
(Lecture 4, Slide 35)
What phosphorylates HMG-CoA reductase?
AMP-activated protein kinase
(Lecture 4, Slide 35)
What is cholesterol transported in the body by?
By body fluid in lipoprotein particles
(Lecture 4, Slide 36)
What is the structure of lipoprotein particles?
They consist of a hydrophobic lipid core, surrounded by polar lipids and proteins
(Lecture 4, Slide 36)
What is “good” and “bad” cholesterol?
HDL (High density lipoprotein) is the good cholesterol
LDL (Low density lipoprotein) is the bad cholesterol
(Lecture 4, Slide 36)
What are bile salts?0
Detergents
(Lecture 4, Slide 37)
Where are bile salts synthesised?
In the liver
(Lecture 4, Slide 37)
Where are bile salts stored and released?
They are stored in the gall bladder and released into the small intestine
(Lecture 4, Slide 37)
What are the 5 classes of steroid hormones?
Progestagens
Glucocorticoids
Mineralocorticoids
Androgens
Oestrogens
(Lecture 4, Slide 38)
What are the 2 steroid hormones in women?
Progesterone and estrogen
(Lecture 4, Slide 39)
