2018 Eukaryotic Cell Structure & Cell Membrane STQ MS.pdf

2018 Eukaryotic Cell Structure and Cell Membrane STQ MS2018 / H2 / ACJC PRELIM / P2 Q11Cholesterol is synthesised in the smooth endoplasmic reticulum (SER) in liver cells by a series of enzyme-catalysed reactions. Cholesterol is then transported to the Golgi apparatus where they are packaged into vesicles and subsequently released into a membrane-bound duct of the liver.Fig. 1.1 is an electron micrograph of a section of a liver tissue. Fig. 1.1(a)Name structure T in Fig. 1.1 and describe its role in liver cells.1.Structure T is the mitochondrion;2.Site of ATP synthesis for synthesis of cholesterol/glycogen (or other liver-specific functions);[2](b)Both prokaryotes and structure T have membrane proteins to help them perform the role described in (a). Suggest how prokaryotes perform this role.1.Presence of electron carriers / ATP synthase; membrane-bound duct ofliverTcholesterol

2.Embedded in cell surface membrane;3.Electron carriers use the energy from the transport of the electrons to pump H+ across the membrane, generating a proton gradient/pool;4.ATP synthase which uses the energy of the proton gradient/proton motive force/flow of protons for chemiosmotic synthesis of ATP;5.AVP;[3](c)Describe the role of cholesterol in the cell surface membrane.Maintain fluidity of the membrane by preventing close packing of phospholipids at low temperature / prevent phospholipids from moving too far apart when temperature is high;[1](d)Suggest how cholesterol is transported from the Golgi apparatus to the membrane-bound duct of the liver.1.Secretory vesicles containing cholesterol pinch off the GA and move along microtubules to the cell surface membrane;2.They fuse with the cell surface/duct membrane and discharge cholesterol outside the cell via exocytosis;[2] [Total: 8]2018 / H2 / IJC PRELIM / P2 Q12Fig. 1.1 shows an electron micrograph of a pancreatic cell that secretes large amounts of insulin that helps to regulate blood glucose level.

A Fig. 1.1(a)With reference to Fig. 1.1, (i)identify organelle A;Golgi apparatus/ body;[1](ii)describe two identifying features of organelle A that allows its identification in (a)(i).1.a stack of discrete, flattened, memb-bound sacs called cisternae;2.distinct memb with 2 faces cis/ convex & trans/ concave);3.vesicles pinching & joining from ends of each sac; (any 2)[2] Fig. 1.2 shows a diagram of the molecular structures of tristearin (a triglyceride) and

phosphatidylcholine (a phospholipid). Fig. 1.2(b)Table 1 shows a structural difference between the two molecules shown in Fig. 1.2.Complete Table 1 with two further structural differences other than in numbers of different types of atoms.Table 1structural featuretristearinphosphotidylcholinelength of fatty acid chainall same lengthdifferent lengthsdegree of saturationall FA tails are saturated1 FA tail is