lecture 4: carbohydrates Flashcards
What is the most abundant class of biomolecules on Earth?
Carbohydrates
Most of carbohydrates’ biomass is produced through…
photosynthesis (from primary producers)
Carbohydrates functions (5) in cells
- Serve as fuels in cellular respiration (glucose)
- Serve as precursors for other organic molecules (ex: amino acids and fatty acids) and building blocks for more complex molecules
- Store chemical energy (as glycogen, starch, so we can use it later)
- Provide fibrous structural materials
- Indicate cell identity and participate in cell communication
Examples of carbohydrates (6)
- Sucrose (disaccharide)
- Starch (energy storage in plants)
- Glycogen (storage in animals)
- Cellulose (structure in cell wall of plants)
- Chitin (structure in cell wall of fungi & exoskeleton in insects)
- Peptidoglycan (structure in cell wall of bacteria)
Carbohydrate structures (4)
- Monosaccharides (1 unit)
- Disaccharides (2 units)
- Oligosaccharides (small chains)
- Polysaccharides (long chains)
Which elements do sugars contain?
C, H, and O
Monosaccharide general structure
Repeating units of C H2 O
- Need at least 3 C
Monosaccharides’ structure can vary in 4 ways:
- Location of carbonyl group (C double bond O): aldehydes (an aldose) at end of carbon chain OR ketones (a ketose) in the middle of carbon chain
- Number of carbon atoms present (3-carbon sugars = trioses, 5-carbon sugars = pentoses, 6-carbon sugars = hexoses)
- Spatial arrangement of their atoms: different arrangement of hydroxyl (OH) groups create stereoisomers isomers —> leading to diff. biological properties
- Linear and alternative ring forms: larger monosaccharides can form ring structures in aqueous solutions
Monosaccharide functions (2)
- Energy-rich molecules used in cellular respiration
- Their carbon skeletons can be used to make other organic molecules
Disaccharide general structure (2 aspects)
- Comprised of 2 monosaccharide monomers (two same or diff.)
- Covalent bond between the two monomers = a glycosidic linkage
How does the structure of disaccharides vary (3)?
- What 2 monosaccharides compose the disaccharide
- Type of bond (alpha or beta)
- Which carbon is involved in the bond
How can the type of bond vary? (2)
Based on:
1. Carbons involved
2. Spatial arrangement of the bond
Disaccharides functions (2 + 2 examples for #2)
- Are breakdown products of polysaccharides
- Can also be produced for transport of energy-rich molecules for cellular respiration
- Sucrose: produced in photosynthetic tissues of plants & transported into non-photosynthetic tissues
- Lactose: produced in milk of mammals to nourish offspring (transport the sugars to offspring)
How can one be lactose intolerant?
- Individuals do not make sufficient amounts of hydrolytic enzyme LACTASE
- So, lactose is not broken down (undigested) and passes through small intestine
- Stays in digestive system and gets fermented
- Lactose gets digested by microorganisms in large intestine and lead to bloating and cramps
What can you do if you are lactose intolerant?
Pills supplying the enzyme lactase in order to hydrolyze lactose
Polysaccharides structures (4)
- Are polymers of monosaccharide monomers
- Can be single chains or branched chains
- Monomers can be same or different
- Types of bonds can vary (alpha or beta)
Polysaccharides functions (2)
2 functional classes:
1. Structural polysaccharides
2. Storage
Why are starch and glycogen (storage polysaccharides) efficient energy-storage molecules? (2)
- Compact: alpha-linkage produce HELICAL chains that can BRANCH
- Easily hydrolyzed: alpha-linkages can be easily broken by hydrolysis when appropriate enzymes are present
STRUCTURE FITS FUNCTION
Why are cellulose, chitin and peptidoglycan (structural polysaccharides) efficient structural molecules? (2)
- Linear: no branching, can interact and form HIGHER ORDER structures
- Resistant to hydrolysis: beta-linkage are NOT easily broken down by hydrolysis bc higher order structures exclude water
STRUCTURE FITS FUNCTION —> provide SUPPORT and PROTECTION
Where does dietary fiber come from?
Cellulose and other indigestible fibrous material from plants
- Can be soluble or insoluble
A high-fiber diet can help: (3)
- Keep digestive system working well
- Maintain healthy weight
- Prevent disease (diabetes mellitus, heart disease, cancer)
What is glycosylation? Where does it occur?
- Adding sugars (oligosaccharides) by covalent bonds to proteins (glycoproteins) and lipids (glycolipids)
- Glycosylation of these molecules occurs in the endomembrane system
Most MEMBRANE proteins and SECRETED proteins are glycoproteins. What are their functions? (2)
- MEMBRANE glycoproteins act as cell identity MARKERS and RECEPTORS (like for blood transfusion)
- SECRETED glycoproteins contribute to the extracellular matrix (ECM) of animal connective tissue and act as HORMONES
How do we differentiate blood groups?
Different and specific glycoproteins expressed at the surface of red blood cells forming different blood groups
(from genetics)
What is blood glucose homeostatis?
When blood glucose is kept within defined limits
What is hypoglycemia? Consequences?
LOW blood sugar
- Starve brain cells and impair brain function —> lead to unconsciousness, seizures, permanent brain damage
What is hyperglycemia? Consequences?
HIGH blood sugar
- Damage blood vessels, nerves, heart, eyes, kidneys
- Can lead to dehydration
What is the receptor and control center for blood glucose homeostasis? And how do they react?
Pancreas (hormone based response)
1. Beta-cells release INSULIN if blood glucose RISES
2. Alpha-cells release GLUCAGON if blood glucose FALLS
What are the effectors of blood glucose homeostasis and what do they do?
- High B.G.:
- Liver (and muscle) takes up glucose and stoares it as glycogen
- Tissues in general take up more glucose - Low B.G.:
- Liver breaks down glycogen and releases glucose into blood
What is diabetes mellitus?
- Condition caused by abnormal homeostatic mechanism.
- Unable to bring glucose levels down into the normal (set-point) range because of abnormal insulin activity.
Difference between Type-1 and Type-2 diabetes mellitus
- Type 1, your pancreas doesn’t make any insulin
- Type 2, your pancreas doesn’t make enough insulin, and the insulin it is making doesn’t always work as it should.
