L3 - Carbohydrates Flashcards
What are carbohydrates?
Biological molecules containing carbon (C), hydrogen (H) and oxygen (O) atoms only.
What is the empirical formula of carbohydrates?
Cm(H2O)n
What is another term for carbohydrates?
- Saccharides
- Sugars
What 3 things do carbohydrates form?
- Rapid and readily available supply of energy
- Form part of important molecules in the cell
- Form markers on the cell surface which aid cell recognition
Describe the 4 classifications of carbohydrates.
- Monosaccharide
- Disaccharide
- Oligosaccharide
- Polysaccharide
Describe the properties of monosaccharides. (x6)
- Single sugar molecules providing instant energy
- Number of carbon atoms ranges from 3-10
- Contain aldehyde / ketone and hydroxyl groups
- Hydroxyl position differs between different sugars
- Sugars can exist in ‘deoxy’ forms (if hydroxyl, OH is replaced with H)
- Exist as open-chain or ring (cyclic) structures joined by covalent bond
Name the 3 aldohexose sugars with the chemical formula C6H12O6.
- Glucose
- Galactose
- Mannose
What are stereoisomers?
Non-superimposable (non-overlapping) mirror images.
What do stereoisomers have in common?
- Same chemical formula
- Same orders and types of bonds
What is different about stereoisomers?
- Different spatial arrangements
- Different biological functions
What is the requirement for stereoisomerisation?
Require at least 1 chiral carbon centre.
What two types of stereoisomers are formed, and do they differ?
- D Isomer: OH on bottom chiral centre points to the right
- L Isomer: OH on bottom chiral centre points to the left
When does cyclisation occur?
When OH group on the second last carbon reacts with a carbonyl group.
What is the resulting product when an aldose is cyclised?
Hemiacetal
What is the resulting product when a ketone is cyclised?
Hemiketal
Name and explain why 2 hemiketal / hemiacetal products come about.
- α anomer
- β anomer
- OH group can attack planar C=O group from either side
Describe the 4 properties of glucose.
- Primary energy source for live
- 7 energy rich C-H bonds
- Bonds broken during cellular respiration
- Released energy is stored as ATP for use by cell
Describe the 4 properties of fructose.
- Important energy source
- 7 energy rich C-H bonds
- Found in fruits, honey, berries and melons
- Forms a furan-based ring structure despite being a hexose
What is furanose?
A 5 membered cyclisation product (pentose sugar).
What are disaccharides?
2 monosaccharides linked together.
Describe the formation of disaccharides.
- Formed by dehydration synthesis (condensation reaction) with the removal of H2O
- Reaction aided by enzymes
- Molecules joined at OH groups by glycosidic links / bonds
- Primary function = nutritional source of monosaccharides
Name the constituents of maltose, and the bonds between these.
- 2 glucose molecules
- Joined at carbons 1 and 4
- α-1,4-glycosidic link
How else can maltose be generated?
Breakdown (hydrolysis) of starch, which is a polysaccharide.
Which enzyme digests maltose?
Maltase
Describe maltose metabolism.
- Metabolised by yeast
- Products: ethanol + CO2
Name the constituents of lactose, and the bonds between these.
- glucose + galactose
- Joined at carbons 1 and 4
- β-1,4-glycosidic link
Which enzyme digests lactose?
Lactase
Name the constituents of sucrose, and the bonds between these.
- glucose + fructose
- Joined at carbons 1 and 2
- α-1,2-glycosidic link
Which enzyme digests sucrose?
Sucrase
What is sucrose abundant in?
Plants and sap - especially sugar cane and sugar beet.
What is a hydrolysis reaction?
Cleavage of chemical bonds by the addition of water.
Describe the 2 types of glycosidic links and where they occur.
- α-1,4-glycosidic link: At the C1 OH group, below the plane of the glucose ring
- β-1,4-glycosidic link: At the C1 OH group, above the plane of the glucose ring
Why might organisms convert soluble sugars into an insoluble form?
- For storage in the cell
- For building structures
- For taking part in cellular processes
What is the range of monosaccharides that may be contained within an oligosaccharide?
3-20
Name the 2 polysaccharide components of starch.
- Amylose
- Amylopectin
Describe the 2 polysaccharide components of starch.
- Amylose: long linear chains of α-1,4 linked D-glucose residues
- Amylopectin: linear chains of α-1,4 linked D-glucose residues joined through α-1,6 linked branch points
What shape is the structure of amylose?
Coiled
What shape is the structure of amylopectin?
Brush-like
Describe the properties of starch. (x3)
- Main dietary source of carbohydrates
- Main storage polymer in plants
- Found in amyloplasts and chloroplasts of plant cells from roots, tubers, seeds and fruits
What are amyloplasts?
Non-pigmented plant cell organelles that are responsible for synthesis and storage of starch granules through polymerisation of glucose.
Which enzymes digest starch, and where are these enzymes found?
- Amylase (in saliva and gut)
- Maltase and Isomaltase (in gut only)
What products is starch digested into?
- Dextrins (oligosaccharides)
- Maltriose
- Maltose
- Isomaltose
- Glucose
What links do amylase and maltase break down?
α-1,4-glycosidic links
What links does isomaltase break down?
α-1,6-glycosidic links
Describe the structure of glycogen.
Complex branched structure of α-1,4 linked D-glucose residues joined through α-1,6 linked branch points.
Describe the differences between the structures of glycogen and amylopectin.
- Structure similar to amylopectin
- But branch points occur more frequently (every 8-12 residues instead of 24-30 residues)
How much glucose does blood typically contain at any given time?
5-6 mMol
How does the body maintain (or attempt to maintain) glucose levels in starving/fasting individuals?
Converts glycogen stores in the liver and muscle to glucose.
What are glycoproteins?
Proteins that contain oligosaccharide chains covalently attached to their protein structure.
What do glycosylated membranes play an important role in?
Immune recognition
What do secreted glycoproteins make up?
- Mucins
- Glycocalyx
What are mucins?
Principle components of mucus by mucous membranes and as component of saliva.
What are mucous membranes?
Lining of body cavities open to the exterior.
What is the glycocalyx?
Glycoprotein covering surrounding the cell membranes of epithelial and other cell types, as well as bacteria.
What are glycolipids?
Lipids that contain oligosaccharide chains covalently attached to their lipid structure.
What are glycolipids often associated with?
Phospholipids on the outer surface of cell membranes.
What do glycolipids usually function as? (x3)
- Recognition signals
- Attachment factors
- Membrane stabilisers
What are sphingolipids?
A sub-type / class of lipids.
What 2 types of sphingolipids are there?
- Ceramide (signalling molecule)
- Sphingomyelin (membranes)
What 2 types of glycosphingolipids are there?
- Cerebosides (found in muscles and nerves)
- Gangliosides (found in plasma membranes)
