Biol110-10-MIDTERM Exam KEY

Biol110-10-MIDTERM Exam KEY - B io l1 1 0 - 1 0 - M id t e...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Biol110-10-Midterm Exam Name ____________ ______________ Exam # KEY_ Biol110 Cell Biology Fall 2010 Midterm Exam Monday Nov 1, 2010 Instructions: Please use a pen (preferably). Write your NAME and EXAM NUMBER in every page. Be brief in each answer, write a full sentence (not phrase) and include key words. Each question is worth 25 points assigned as indicated. Use only the backside of the question page for extra writing space if needed. This is a closed book & notebook exam. Grading: Question #1 __25____ Question #2 __25____ Question #3 __25____ Question #4 __25____ Total Score __100__ Letter Grade __A+ __
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Biol110-10-Midterm Exam Name ____________ ______________ Exam # KEY_ Question #1 : Membranes and Porins What makes phospholipid membranes planar (2 pts) and highly fluid yet structurally cohesive (1 pt)? Why does water have a tendency to rush into cells? (2 pt) How have cells adapted to this constant water assault? (2 pts) The cylindrical geometry of the phospholipid molecules and their lateral stacking makes membranes planar while their non-covalent interactions and fast dynamics allows them to remain fluid (in constant motion) yet cohesive. Water has a tendency to rush into cells by osmotic effects, as the concentration of solutes inside cells is usually higher than outside. Cell have adapted to this problem by building cell walls, or by pumping ions out of cells, or by extruding water in membrane vesicles. What are biological membranes permeable to? (2 pt) What governs the strength of interaction between phospholipid molecules? (2 pts) Human cells contain a 1:1 ratio of cholesterol to phospholipid in the plasma membrane; what structural and/or functional advantage does its presence confer at 37°C? (2 pts) Biological membranes are fully permeable to small, non-polar (hydrophobic), uncharged molecules. The strength of interaction between phospholipid molecules is governed by temperature, the length of the fatty acid tail of its phospholipids and their degree of saturation. Cholesterol occupies ‘dead space’ between phospholipid molecules in membranes to improve their stacking, and to make them less leaky against ions at physiological temperature. From examining amino acid sequence alone, how can you tell if a protein resides in a cellular membrane? (2 pt) What other forms of membrane attachments are not obvious from sequence alone? (2 pts) If biomembranes are fluid, how can their proteins be restricted to a particular membrane location? (2 pts) Using a hydropathy plot one could determine if a particular protein has a continuous stretch of ~20 AA, which is sufficient to serve as a transmembrane domain. Proteins could also be attached to membranes via fatty acid tails, or using a beta barrel configuration, or peripherally via ionic interactions. The mobility of proteins in membranes can be restricted by corralling, or by tethering to an intracellular scaffold, or by interacting with others transmembrane proteins of an adjacent
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/17/2011 for the course BIOL 110 taught by Professor Rexach during the Fall '10 term at UCSC.

Page1 / 5

Biol110-10-MIDTERM Exam KEY - B io l1 1 0 - 1 0 - M id t e...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online