Lecture 5 - Carbohydrates And Nucleic Acids Flashcards
What are the 2 kinda of oligosaccharide linkages in glycoproteins?
When do they each occur?
N linked and O linked
N linked occurs co-translationally (in ER)
O linked occurs post translationally (golgi)
What are the 3 major functions of protein bound oligosaccharides?
1) assist in chaperone folding by providing a recognition site for the chaperone
2) provide specific oligosaccharide tags for protein binding
3) provide blood group specificity
What are lectins? What do they do?
Lectins is the general name for proteins that bind to carbohydrates tags
They prevent mislocalization of lysosomal enzymes, control the rate of degradation of peptide hormones and mediate binding of pathogens go cellular targets
What are 2 common locations of proteoglycans?
Cartilage and the cell membrane
What is the structure of proteoglycans found in the membrane?
A core membrane protein with covalently attached glycosamimoglycans on outer surface of cell
What is the function of the extra cellular domain of membrane proteoglycans
To bind proteins and signaling molecules and alter their activity
How do glycosamimoglycans attached to membrane proteoglycans alter the activity of bound proteins?
Binding of proteins to GAG causes conformational change in proteins. Also binding of multiple proteins to GAGs puts them in close proximity to react / bind. Binding to GAG can increase local concentrations of signaling molecules thus enhancing interactions with receptors on the cell
How are nucleotides linked together by phosphodiester bonds?
Phosphate groups link the 3’ carbon of one sugar to the 5’ carbon of another sugar
5’ end of DNA has free ___
3’ end of DNA has free ___
Phosphate group on 5’ sugar
OH group on 3’ sugar
What is the difference between DNA and RNA with respect to the hydroxyl groups?
RNA has OH at 2’ position DNA does not
What are the 7 major features of DNA helix?
1) strands are antiparallel
2) DNA has a sugar phosphate backbone with negative phosphate groups exposes to solvent
3) nitrogenous bases are in the middle of the helix and interact with each other via hydrogen bonds between bases on opposite strands
4) there is a major and a minor groove
5) the helix completes a turn about every 10th base pair
6) the base pairs stack on top of one another creating a solid core
7) DNA is right handed helix
What are stacking interactions?
In center of helix, base pairs stack on top of one another with their rings parallel to one another so they are attracted via van der waals forces and hydrophobic interactions. The stacking interactions are stronger for G and C pairs than A and T
Are hydrogen bonds or stacking interactions responsible for holding the helix together?
Stacking interactions.
Hydrogen bonds hold the 2 strands together and create the 2ndary structure of the helix but the stacking is what holds the whole structure in its folded state
Difference between B A and Z helices?
B is most common in physiologic conditions. Right handed double helix
A is found under dehydration conditions in lab. Right handed double helix but wider than B
Z is left handed double helix, lots of repeating GCGC sequences, thinner than B and less ordered
What is Tm of DNA on graph?
Mid point of linear portion of DNA melting curve
