SI Anna Betz annabetz umass edu Bio 151 Professor Moscarella Sessions Tuesday and Thursday 5 30 6 45 PM Library 1201 Session 1 Material from Lecture 2 Characteristics of Cells We talked about three distinct characteristics of cells the plasma membrane genetic information and metabolism State which characteristic matches the following features Produces ATP by obtaining and transforming energy Metabolism the sum of reactions that occurs within each cell that helps provide energy for the body The energy that is produced is used for different bodily processes as well as synthesis of new organic material such as proteins carbs lipids and nucleic acids Separates and protects the cell from its external environment Plasma membrane also allows for selective passing of molecules selective permeability Blueprint for the cell to grow function and reproduce Genetic information information in DNA is stored as the pattern of different bases A G C T Aids in communication and homeostasis Plasma membrane because the membrane has selective permeability it is able to regulate the passing of certain molecules which helps allow it to maintain a stable internal environment homeostasis Fluidity is important in cell communication Viruses In class we learned that viruses are not living cells Which of the following helps to support this conclusion 1 They are unable to reproduce without the aid of a host cell 2 They are unable to make their own energy 3 They can only produce ATP with the aid of a host cell 4 Both 1 and 2 5 All of the above Viruses are not able to reproduce on their own they rely on the host cell s machinery in order to reproduce They are also unable to synthesize ATP and can t metabolize make energy which is the main reason viruses are not alive 3 is incorrect because viruses are never able to produce ATP they don t have the correct machinery Instead they rely on the host cell s energy to carry out their processes SI Anna Betz annabetz umass edu Plasma Membrane Bio 151 Professor Moscarella Sessions Tuesday and Thursday 5 30 6 45 PM Library 1201 The plasma membrane is composed of many phospholipids These phospholipids have a hydrophilic head and a hydrophobic tail Because they have two distinct regions in one molecule phospholipids are considered amphipathic Using the diagram above which parts of the intrinsic protein would you expect to be hydrophobic Which parts would you expect to be hydrophilic The part exposed to the inside of the membrane would be hydrophobic This part of the protein does not want to be exposed to water The extracellular outside of the cell and intracellular inside of the cell domains would both be hydrophilic The interior of the channel would also be hydrophilic because it needs to be able to transport water ions Where would you expect to find the polar part of a phospholipid to appear in the plasma membrane Polar molecules are hydrophilic molecules so you would expect it to be facing the aqueous environment on the outside of the membrane Non polar molecules are hydrophobic so those would appear inside the membrane SI Anna Betz annabetz umass edu Bio 151 Professor Moscarella Sessions Tuesday and Thursday 5 30 6 45 PM Library 1201 Label the following fatty acid tails as either saturated or unsaturated Top is saturated and bottom is unsaturated Unsaturated fatty acid tails have one or more double bonds in them You are analyzing a plasma membrane and notice many unsaturated fatty acids What does this tell you about the membrane fluidity More unsaturated fatty acids means the cell membrane is more fluid because the double bonds form kinks in the phospholipids which means they cannot pack as tightly Suppose you are studying the cell membrane of two populations of the same organism One population is found in an environment where it is cold and snowy year round The other population lives in an environment that is warm and sunny Describe what you would expect each population s cell membrane to look like in order to maintain homeostasis In order to maintain homeostasis the population that lives in a colder environment would be more likely to have shorter unsaturated fatty acid tails in order to prevent dense packing of phospholipids and help maintain a little fluidity Shorter tails make less interactions with each other which makes the membrane more fluid The population that lives in a warmer environment would be more likely to have longer saturated tails in order to prevent the cell membrane from becoming too fluid Longer tails make more interactions with each other which makes the membrane more viscous SI Anna Betz annabetz umass edu Which of the following are true about cholesterol select all that apply It acts as a channel for certain molecules to cross the membrane It acts as a buffer to keep the membrane fluid as external temperatures change Bio 151 Professor Moscarella Sessions Tuesday and Thursday 5 30 6 45 PM Library 1201 1 2 a At lower temperatures it prevents the membrane from solidifying helps keep phospholipids separated at higher temperatures it prevents the membrane from becoming too fluid prevents movement of phospholipids by stabilizing them 3 It is only found in animal cells a True in plants sitosterol regulates membrane fluidity permeability 4 You typically have more production of cholesterol in the colder temperatures a In colder temperatures the cell membrane is more likely to become densely packed so in order to combat this more cholesterol is produced Draw a graph of what you would expect membrane fluidity levels to look like as temperature decreases As temperatures decrease you would expect there to be less fluidity This is because lower temperatures causes phospholipids to become more densely packed which makes the membrane less fluid SI Anna Betz annabetz umass edu Which of these factors CAN be changed by cells Bio 151 Professor Moscarella Sessions Tuesday and Thursday 5 30 6 45 PM Library 1201 1 Cholesterol content 2 Types of fatty acids 3 External temperature 4 Membrane fluidity A Only 3 B 1 and 2 only C 1 2 3 and 4 D 1 2 and 4 only 1 2 and 4 can all be changed by cells in order to help maintain homeostasis External temperature would be what induces these changes in cells As an organism s body heats up what can we expect of the plasma membrane in order to maintain homeostasis 1 An increase in phospholipid fatty acid side chain length and an increase in side chain 2 A decrease in phospholipid fatty acid side chain length and a decrease in side