MCB 181 1st Edition Lecture 9 Outline of Previous Lecture I. LipidsII. Permeability of a Lipid BilayerIII. Clicker QuestionsOutline of Current Lecture I. Membrane ProteinsII. Clicker QuestionsCurrent LectureI. Membrane Proteinsa. In a lipid bilayer, there exists amphipathic proteins – proteins which have both hydrophobic and hydrophilic endsb. There are three broad groups of transmembrane proteins i. Channel proteins – highly selective and highly regulatedii. Transporters – also known as carrier proteins as they change their shape during the process of facilitated diffusioniii. Pumps – use energy to move particles against an electron gradient c. Passive transport – produced by diffusion along an electrochemical gradient and doenot require an expenditure of energyd. Facilitated diffusion – the passive transport of substances that otherwise would not cross a membranee. Active transport – the movement of a substance across a cell membrane against the concentration of an electrochemical gradienti. Requires energy and specific transport moleculesII. Clicker QuestionsThe sea gull drinks seawater when fresh water is limited and to save itself from dehydration,the bird excretes salt from its nostrils.Assertion ReasonWithout these glands the gull will die from dehydration.BecauseDuring osmosis water moves from an area of low solute concentration to an area of high solute concentration.Assertion is true; Reason is true; reason is the correct explanation.Assertion ReasonThe membrane of the cells in these glands contain a high concentration of pumps because the salt molecules are moving by active transport from the blood stream to the gland.BecauseWhen molecules move from high concentration to low concentration, energy must be spent.Assertion is true; Reason is
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