unit 1 week 4 info Flashcards
What are the 4 types of biological molecules?
Carbohydrates, lipids, proteins, nucleic acids
What do carbohydrates primarily function as?
Stores of chemical energy and as durable building materials for biological construction
What are the types of simple sugars based on the number of carbon atoms?
Trioses, tetroses, pentoses, hexoses, heptoses
What does each sugar molecule consist of?
A backbone of carbon atoms linked together in a linear array by single bonds
What is linked to each carbon atom in the sugar backbone?
A single hydroxyl group, except for one that bears a carbonyl (C=O) group
What form do most sugar molecules take in solution?
The ring form
Why is the linear form of sugar biochemically important?
The aldehyde group at the end of the chain can react with proteins
What is the maximum number of atoms a carbon atom can bond with?
4
What increases as the backbone of sugar molecules increases in length?
The number of asymmetric carbon atoms and number of stereoisomers
How are sugars labeled as D or L?
Based on the arrangement of groups attached to the asymmetric carbon atom farthest from the aldehyde
What distinguishes between D and L sugars?
Enzymes
How can sugars be joined together?
By covalent glycosidic bonds to form bigger molecules
What forms glycosidic bonds?
A reaction between carbon atom C1 of one sugar and the hydroxyl group of another sugar
What are molecules composed of two sugar units called?
Disaccharides
What is the primary function of disaccharides?
To serve as readily available energy stores
What is sucrose and where is it found?
Sucrose is table sugar and a major component of plant sap
What role does sucrose play in plants?
It carries chemical energy from one part of the plant to another
What is lactose and where is it found?
Lactose is a sugar found in the milk of most mammals
What does lactose provide for newborn mammals?
Fuel for early growth and development
What enzyme hydrolyzes lactose in the diet?
Lactase
Where is lactase found?
In the plasma membranes of the cells that line the intestine
What happens to lactase levels in many people after childhood?
They lose the enzyme and may experience digestive discomfort when eating dairy
What are small chains formed by linking sugars together called?
Oligosaccharides
What did Bernard find about glucose and glycogen?
Glucose enters blood from liver, and liver tissue has glycogen
What maintains blood glucose levels according to Bernard’s hypothesis?
Balance between glycogen formation and breakdown in the liver
What did Bernard name the molecule he discovered?
Glycogen
What type of molecule is glycogen?
Polysaccharide
How is glycogen formed?
Polymer of sugar units joined by glycosidic bonds
What type of polymer is glycogen?
Branched polymer of glucose
What type of glycosidic bonds join sugar units in glycogen?
(1 → 4) and (1 → 6) glycosidic bonds
What does glycogen serve as in animals?
A storehouse of surplus chemical energy
How long can glycogen fuel human skeletal muscles?
About 30 minutes of moderate activity
What is starch made of?
Polymer of glucose, mixture of amylose and amylopectin
What is the difference between amylose and amylopectin?
Amylose is unbranched, amylopectin is branched
How is starch stored in plants?
In starch grains within plastids
What is cellulose?
A structural polysaccharide made of glucose with (1 → 4) linkages
What is cellulose used for?
Component of plant cell walls and durable materials like cotton and linen
Why can animals not digest cellulose?
They lack the enzyme cellulase, but some harbor bacteria or protozoa that produce it
What type of polymer is chitin?
Unbranched polymer of N-acetylglucosamine
What is another group of polysaccharides with a complex structure?
Glycosaminoglycans (GAGs)
What are lipids?
Diverse group of nonpolar biological molecules that can dissolve in organic solvents and are unable to dissolve in water
What are fats composed of?
Glycerol molecule linked by ester bonds to three fatty acids
What is the composite molecule of fats called?
Triacylglycerol or triglyceride
What is the structure of a fatty acid?
Long, unbranched hydrocarbon chain with a carboxyl group at one end
What describes molecules with both hydrophobic and hydrophilic regions?
Amphipathic
Why are amphipathic molecules biologically important?
They have unique properties due to their differing regions
What are saturated fatty acids?
Fatty acids with no double bonds, e.g., stearic acid
What are unsaturated fatty acids?
Fatty acids that have double bonds, e.g., linoleic acid
What configuration do natural double bonds have?
Cis configuration
What effect do double bonds have on fatty acid chains?
Cause kinks, preventing tight packing and lowering melting temperature
Why are vegetable fats liquid at room temperature?
They contain many double bonds, making them polyunsaturated
What are oils?
Fats that are liquid at room temperature
How are solid shortenings like margarine made?
By hydrogenating unsaturated vegetable oils, creating trans fats
Why are trans fats harmful?
They increase risk of heart disease
How much energy does fat contain?
Twice the energy of carbohydrates per gram
How is fat used for energy?
Long-term energy storage
How much fat does an average person have?
About 16 kg, providing 144,000 kcal
How do fats compare to carbohydrates in terms of energy availability?
Fats provide long-term storage, carbohydrates are short-term energy
Why are fats insoluble in water?
They lack polar groups
How are fats stored in cells?
As dry lipid droplets in adipocytes
What is the structure of steroids?
Four-ringed hydrocarbon
What is a key steroid in animals?
Cholesterol
What is cholesterol’s role?
Cell membrane component, precursor to hormones
What hormones are derived from cholesterol?
Testosterone, progesterone, estrogen
Is cholesterol found in plants?
No
Why are vegetable oils ‘cholesterol-free’?
Plants lack cholesterol
What is the structure of phospholipids?
2 fatty acids, diacylglycerol backbone
What attaches to glycerol’s third hydroxyl in phospholipids?
Phosphate group
What bonds to the phosphate group in phospholipids?
Polar group like choline
What are the two ends of a phospholipid?
Hydrophilic phosphate, hydrophobic fatty acids
What are membranes made of?
Lipid-protein assemblies held by noncovalent bonds
What forms the core of membranes?
Lipid bilayer, which forms a barrier to water-soluble materials
What do membrane proteins perform?
Specific functions unique to cell type
What varies by cell type and function?
Lipid-to-protein ratio
What do membranes contain besides lipids and proteins?
Oligosaccharides attached to lipids and proteins
What are the three main types of membrane lipids?
Phosphoglycerides, sphingolipids, and cholesterol
What are phosphoglycerides built on?
A glycerol backbone
What are sphingolipids derived from?
Sphingosine, an amino alcohol with a long hydrocarbon chain
What do sphingolipids consist of?
Sphingosine linked to a fatty acid, forming a ceramide
What is cholesterol’s role in membranes?
A lipid in some membranes, making up to 50% of the plasma membrane in animal cells
What does the rigid structure of cholesterol disrupt?
Movement of phospholipid fatty acid tails
What is the importance of the lipid bilayer?
Helps maintain the cell’s internal composition and plays a role in various cellular activities
What is the asymmetry of membrane lipids?
The lipid bilayer has two distinct leaflets
What is found in the outer leaflet of the lipid bilayer?
Higher concentration of phosphatidylcholine (PC) and sphingomyelin
What is found in the inner leaflet of the lipid bilayer?
Higher concentration of phosphatidylethanolamine (PE) and phosphatidylserine (PS)
What do carbohydrates in plasma membranes constitute?
2-10% of membrane weight
What are the majority of carbohydrates linked to in membranes?
Proteins (glycoproteins) and some to lipids (glycolipids)
What is the function of carbohydrates in membranes?
Mediate cell-environment interactions and protein sorting
What determines blood type?
Carbohydrate modifications on glycolipids
What are the three classes of membrane proteins?
Integral proteins, peripheral proteins, lipid-anchored proteins
What is a transmembrane protein?
Integral membrane protein that spans the lipid bilayer
What are peripheral membrane proteins associated with?
The membrane by weak noncovalent bonds
What are the characteristics of integral membrane proteins?
Integral membrane proteins are lined with hydrophilic residues, can move laterally within the membrane, and penetrate membranes rather than staying external.
They reveal integral membrane proteins when the bilayer is split.
What does freeze-fracture replication reveal?
Freeze-fracture replication shows membrane microheterogeneity and the separation effect of integral membrane proteins, which leave pits in the other half of the membrane.
What are peripheral membrane proteins?
Peripheral membrane proteins are associated with the membrane by weak noncovalent bonds, can be solubilized with high-salt solutions, and provide mechanical support and varied roles such as enzymes or signal transducers.
What are lipid-anchored membrane proteins?
Lipid-anchored membrane proteins are bound to the membrane by a lipid anchor, such as GPI-anchored proteins attached via glycosyl-phosphatidylinositol, and cytoplasmic lipid-anchored proteins linked by hydrocarbon chains.
What challenges exist in studying integral membrane proteins?
Integral membrane proteins are difficult to isolate due to hydrophobic transmembrane domains and require detergents for removal, such as SDS and Triton X-100.
What is the function of hydropathy plots?
Hydropathy plots identify transmembrane segments by measuring hydrophobicity along the polypeptide, showing jagged peaks in the hydrophobic spectrum.
What are the characteristics of transmembrane domains?
Transmembrane domains consist of about 20 nonpolar amino acids forming an alpha helix, with hydrophobic side chains dominating and charged residues typically at the ends.
How can site-directed mutagenesis be used?
Site-directed mutagenesis can identify accessible sites in transmembrane domains, with NEM alkylating cysteine residues if they are accessible to the aqueous environment.
What is the significance of membrane fluidity?
Membrane fluidity allows for mobility, structural organization, and interaction, which are crucial for processes like cell movement, growth, division, and secretion.
How do cells maintain membrane fluidity?
Cells maintain membrane fluidity by altering phospholipid types, desaturating fatty acids, reshuffling fatty acids, and synthesizing more unsaturated phospholipids.
What are lipid rafts?
Lipid rafts are cholesterol and sphingolipid microdomains that are more ordered and gel-like than surrounding regions, proposed to concentrate specific proteins and organize the membrane.
