Lecture 12 Flashcards
What is an extremely common strategy to modify enzymes and protein activity?
– covalent modifications
T or F, covalent modifications are often reversible and are done by enzymes which are themselves subjected to regulation
True
Describe phosphorylation by kinases and dephosphorylation by phosphatases.
– utilize an ATP that adds a PO4 to a specific amino acid on an enzyme –> phosphorylation
– dephosphorylation is removal of phosphate by phosphotases
What are zymogens?
– inactive forms of enzymes aka proenzymes
How does regulation with zymogens work?
– zymogens are activated into enzymes by proteolytic cleavage (protease activation)
– Synthesized in pancreas and secreted into duodenum in small intestine
- enter as inactive forms and get converted to active proteases in small intestine
- ensures active enzymes are only in lumen and not in pancreatic cells
T or F, trypsin is a common activator of many zymogens
True
What is trypsin?
– a common activator of multiple zymogens for enzymes involved in protein degradation and more generally in digestive functions
T or F, zymogens activation by trypsin provides strong and synchronized commitment to digestion of proteins
True
Why are good inhibitors needed for trypsin?
– because zymogen activation is irreversible, good inhibitors are needed to block key activators such as trypsin
Ex: Pancreatic trypsin inhibitor regulate trypsin activity
How does trypsin active chymotrypsin?
– It cleaves at the 15/16 site that results in the formation of the pi chymotrypsin.
– This further cleaves to form a triad by the release of two dipeptides.
– This results in the alpha chymotrypsin, the most active chymotrypsin, and results in a A, B and ,C chain that contain the serine residue, histidine, and Aspartate amino acid.
What are other important biological cascades involving zymogens?
- Blood clotting
- Caspases: enzymes involved in cell apoptosis
- Protein hormones: Insulin is derived from pro-insulin
- Collagen is derived from procollagen
What are the general functions of carbohydrates?
- They act as cellular protection,
- generate and store biological energy, – serve as molecular recognition analogs, – cell signaling
- cell adhesion
- biological lubrication
- control of protein trafficking, and – maintenance of biological structure.
What is the general molecule formula for carbohydrates?
(CH2O)n
T or F, elemental analysis of carbohydrate yield one H2O molecule for every C atom
True
T or F, carbohydrates have a very large structural diversity
True
What are monosaccharides typically used for?
as fuel and as building blocks for synthesis of complex molecules like dna, glycoproteins, storage molecules
What’s the difference between an aldose and ketose sugar?
an aldose sugar has a sugar with the 1 carbon containing an aldehyde group. A ketose sugar has a ketone group somewhere along its chain. This ketone group is not carbon 1.
What is the most common form of stereoisomer of sugars in living organisms?
D sugars
True or false. Monosaccharides with 3 carbons or more contain 1 or more chiral carbons.
True
How do we assign D/L isomers for carbohydrates?
– the position of the last chiral carbon from the carbonyl group.
– If the last chiral carbon contains the OH to the right, it is a d sugar.
– If the last chiral carbon contains an OH to the left, it is an L sugar.
True or false.
At equilibrium, carbohydrates are typically in their cyclic form
True
True or false.
Furan are 5-membered sugar sings that result from the 4C alcohol attacking the 1C carbonyl group
True
True or false?
Pyranose is made from the attack of the C5 sugar on the C1 carbonyl to give a 6 membered sugar ring.
True
Which carbon in a sugar is considered the anomeric carbon?
C1
What is an anomeric carbon? How does this relate to sugars?
– Carbon that can readily change between different epimers ( molecules that differ only by one stereocenter) by forming the open chain intermediate and form the other epimer.
–If there is a hemiacetal on the sugar ring, it can open and change from the alpha or beta sugar.
True or false.
The alpha sugar form has its alcohol in the hemiacetal forming upwards whereas the beta has it pointing downward
False. alpha has it pointed downward and the beta is pointed up
How can you tell whether an open chain sugar will form an alpha or beta epimer?
– If the C1 alcohol in the open chain is on the right, it is alpha.
– If the C1 alcohol is pointing to the left, it is beta
What are common derivatives of monosaccharides
methylation, acetylation, and phosphorylation
What makes a sugar a reducing sugar?
having a hemiacetal allows it to be a reducing sugar. This allows it to open and be in a more readily oxidizable form.
*note: reducing sugar loses electrons
What does reducing sugar mean?
It means it is able of being oxidized and reduce other stuff. It is equivalent to saying it is a reductant.
Why can’t an acetal be reducing?
It will be locked into its ring conformation, which is oxidizable because it needs to be open in order to be oxidized effectively
What are the types of glycosidic bonds?
O-glycosidic or N-glycosidic
What is the main difference between glycogen and amylopectin?
– Glycogen has branching every 10-12 residues
– whereas amylopectin branches every 30 residues.
– Therefore glycogen is more branched.
Whats the difference between amylose and amylopectin?
amylose has no branching
Why are glycogen/amylopectin good storage molecules?
Branching allows good storage in a small area, allows for glucose stores to remain inside the cell and not diffuse out since it is good for cell, and it osmotically inactives glucose.
Why is cellulose different than Gylcogen?
– cellulose has beta 1-4 bonds and is linear in structure. This allows it to have fiber like structures with high intra-fiber hydrogen bonding.
– The glycogen branching of alpha 6 favor packing whereas the beta favor strengthening.
What are glycoproteins?
proteins modified with carbohydrates by the ER/golgi at specific AA.
Which specific AA allow for glycosidation?
Asn for N-glycosidic and Ser/Thr for O-glycosidic.
Specifically, for N-glycosylation, you need Asn-X-Ser or Asn-X,Thr where X can’t be proline
Which enzyme allows for glycosidation?
glycosyltransferase puts a carbohydrate on a protein to make it a glycoprotein.
True or False.
O phenotypes have a mutated glycosyltransferase enzyme
true
What type of glycosyl is transferred via the A type glycosyltransferase?
N-acetylgalactosamine
What type of glycosyl is transferred by B type?
galactose
True or false. O blood type makes anti a and B antibodies
true
What is EPO?
– glycoprotein involved in stimulating RBC production through its 3x N-glycosylated asn residues and 1x
O-glycosylated Ser residues.
– This pattern prevents degradation and stimulation of RBC
What type of glycosylation patterns do mucins have?
Ser/Thr o linked glycosylation
What are functions of mucins?
cell adhesion, fertilization, barrier to pathogens
Why are reducing properties important?
- for forming polysaccharides chains
- - for non specific reaction with other molecules (e.g. glycosylation in aging)
How can reducing properties be blocked?
– by locking carbohydrates in their cyclic form (e.g. methylation)
What is the difference between hemiacetal and acetal linkages?
- hemiacetal can open
- - acetal linkages are locked
