MEDF 1011 Cell Membrane and Cell Organelles PDF

MEDF 1011 Foundation Course for Health Sciences I The Cell Membrane and Cell Organelles Dr. Yeung Hang Mee, Po School of Biomedical Sciences Email: [email protected] Office: Choh-Ming Li Basic Medical Sciences Building...

MEDF 1011 Foundation Course for Health Sciences I The Cell Membrane and Cell Organelles Dr. Yeung Hang Mee, Po School of Biomedical Sciences Email: [email protected] Office: Choh-Ming Li Basic Medical Sciences Building 6/F Room 610P 1  Learning Objectives Describe the characteristics of a living cell membrane; Overview of membrane permeability and its biological importance; List examples of cell organelles with or without membranes; Explain the structures and functions of different cell organelles. 2  Biomolecules to supply cellular use in our body DNA Double Helix H C O N S P Hydrocarbons Carbohydrates and Lipids Amino Acids and Proteins Nucleic Acids, DNAs and RNAs Reference: Basic Concepts in Biomedical Sciences I. 3 Representative Cell Types in Human Body energy storage, break down when emergency use of energy required Reference: Human Physiology: An Integrated Approach. 4 General Structure of A Human Cell 5 What Is A Cell Membrane? 6  Cell Membranes as Selective Barriers As a boundary to: Separate cytosol from extracellular fluid; Enclose individual organelles; Prevent mixing of different biomolecules. Permeable to selective substances: To control required molecules getting into a living cell; To be regulated by presence of membrane proteins. 7 The Structure of Cell Membrane 8  phospholipid outside to interact better with bloodstream The Structure of Cell Membrane 9  Compositions of Cell Membrane Lipid molecules: Proteins: Phospholipid (relatively Integral type (completely embedded in bilayer) negative charged) Peripheral type (just at the surronding) Cholesterol Cholesterol (27-carbon biomolecule) 10 Membrane Asymmetry & Fluid Mosaic Model 11  What Is Membrane Asymmetry? not symmetric The compositions of two membrane layers of a living cell are different! cell recognition The sugar side chains (glyco-) are always at the outer face of membrane: Sugar + lipid: glycolipid Sugar + protein: glycoprotein Reference: Essential Cell Biology. 12 Biological Importance of Glyco- Molecules Reference: Molecular Cell Biology 6th Edition. 13  Mobility of Lipid Components in Membranes mobile in nature The cell membrane is not very rigid in nature! A. Rapid rotation: Rotation around the hydrophobic tail. B. Flip-flop exchange: Relatively slow due to the thermodynamic constraints. C. Rapid lateral diffusion: Exchange places with neighbouring molecules in the same layer; Proteins are also free to move laterally. Reference: Becker’s World of the Cell. 14  The Fluid Mosaic Model Imagine the membrane is a fluid in nature: Lipids and proteins are able to move laterally. The membrane is described as a “sea”. The fluidity can be increased with: Surrounding temperature (why?) Increased carbon-carbon double bonds (-C=C-) on the hydrocarbon chain (why?) messier -> less packed Less cholesterol (why?) cholesterol is sticky in nature, therefore less cholestrol can increaser fluidity Hyper-:above normal level The membrane is described as a Hypo-: Below normal level “mosaic” model: Membrane proteins are dispersed throughout the membrane. increase, as when the lipids are of high temeperatiure, their KE is increased, thus increasing fluidity 15 and movement Biological Functions of Membrane Proteins 16 Biological Functions of Membrane Proteins To act as the protein receptors: Enable cells to respond to hormones, neurotransmitters etc. Example: insulin (peptide hormone from pancreas) binds with insulin receptor on skeletal muscle cell. highly sensitive to insulin (no.4) 17 Biological Functions of Membrane Proteins To act as adhesion molecules: Connect the neighboring cells; Provide mechanical strength and support to the cells. 18  Biological Functions of Membrane Proteins To act as an enzyme (biocatalyst): Facilitate the biochemical reactions or pathways during metabolism in a living cell. Example: synthesis of adenosine triphosphate (ATP) by mitochondrial ATP synthase. ATP Structure of Adenosine Triphosphate 19  Biological Functions of Membrane Proteins To allow transport of substances across the membrane: Permeable to: gas molecules; small uncharged molecules. Impermeable to: Ions carrying positive or negative charges; Large uncharged molecules especially water-soluble in nature; 20  Biological Functions of Membrane Proteins How can glucose (as a fuel to our human body) and ions be transported into a living cell? By transporter By ion channel By pump 21 Cell Organelles 22 Inner Structures of A Living Cell 23  The Cell Nucleus Information centre to store genetic information by biomolecule deoxynucleic acid (DNA). DNA -> gene -> chromosome inside cell nucleus. Reference: University London College - Institute of Ophthalmology 24  The Cell Nucleus Different parts inside nucleus: Nuclear envelope: Double layers of membrane to form the envelope; Have pores to exchange materials. Nucleolus: Synthesis of ribosomes Nucleoplasm: Contains 23 pairs of chromosomes which the last pair determines the sex of human body. 25  The Cytoplasm The cytoplasm is defined as all materials inside a living cell except the cell nucleus. It consists of: Cytosol: jelly-like fluid filling the cell Organelles: With membrane: Endoplasmic reticulum Golgi Body Lysosome Mitochondria Without membrane: Ribosome Cytoskeleton (protein) 26  Endoplasmic Reticulum There are two types of endoplasmic reticulum (ER): Smooth ER Rough ER Ribosome Reference: https://www.shmoop.com/study- guides/biology/biology-cells/all-eukaryotic-cells 27  Smooth Endoplasmic Reticulum “Smooth” means the ribosomes are absent at the surface of ER. 80% from body Functions: Synthesis of lipid: Cholesterol is synthesized by enzymes at the smooth ER of liver cells (hepatocytes). Drug detoxification: Alcohol is metabolized by enzymes at the smooth ER of liver cells. Intracellular calcium storage: intracellular calcium ions will be released from ER in muscle cells during contraction. 28  Rough Endoplasmic Reticulum “Rough” means the ribosomes are present at the surface of ER. The rough ER is continuous with the outer membrane of nuclear envelope. Functions: Protein synthesis; Modifications of newly synthesized protein such as glycosylation to make glycoprotein. 29  Nucleus Translation Transcription mRNA 1 mRNA is produced in DNA the nucleus and moves through the nuclear pore into the cytoplasm 2 Ribosomal In the cytoplasm, the subunits mRNA and ribosomal mRNA subunits join, and protein synthesis begins. 3 After a ribosome attaches to a receptor on the rER, the protein enters the ribosome lumen of the ER. Receptor rER membrane mRNA 4 Ribosomal subunits and mRNA break away. The protein remains in the rER and folds into its final shape. Lumen of rER Protein rough Endoplasmic Reticulum (rER)  The Golgi Body The Golgi body is also called Golgi apparatus. A processing station that participates in protein maturation and targets newly synthesized proteins to their appropriate subcellular destinations. Two networks: Cis- network: receiving vesicles from rough ER. Trans- network: releasing vesicles towards cell membrane for secretion. Reference: microbiologynote.com 31  The Lysosome It contains enzyme (lysozyme) to catalyse the breakdown of intracellular unwanted substances. It carries hydrogen ion (H+) pumps to deliver intracellular hydrogen ions into lysosome. Thus the lysozyme will be activated under acidic environment (pH 4.5 – 5.5). Reference: cartage.org.lb/zoology 32  The Lysosomal Storage Disease (LSD) This disease is the genetic disorder leading to accumulation of intracellular unwanted molecules and swelling of cells. Example: Tay-Sachs Disease cannot generate new neuron to repair / replce Infants with this disease (at age 3-6 months) will lose the motor skills and grow up with seizures, vision and hearing loss and paralysis. An eye abnormality called a cherry-red spot on retina is one of the characteristics of this disorder. Reference: Lehninger – Principles of Biochemistry. 33  The Mitochondria It generates the adenosine triphosphate (ATP) as the energy- carrying molecule in the cells. Characteristics of mitochondria: Two layers of membranes (inner and outer). Inner membrane contains lots of proteins responsible for ATP production. Reference: Lehninger – Principles of Biochemistry. 34  The Mitochondria It generates the adenosine triphosphate (ATP) as the energy- carrying molecule in the cells. Characteristics of mitochondria: Matrix is responsible for the fatty acid oxidation (energy release) and protein metabolism (urea cycle). Reference: Lehninger – Principles of Biochemistry. 35  The Mitochondria It generates the adenosine triphosphate (ATP) as the energy- carrying molecule in the cells. Characteristics of mitochondria: Mitochondrial DNA is responsible for encoding proteins for ATP production. Circular DNA vs. double-stranded helix of DNA inside cell nucleus. Reference: Lehninger – Principles of Biochemistry. 36  The Mitochondria It also involves in programmed cell death (apoptosis) pathways to eliminate unwanted cells. Examples: turnover of old/aging red blood cells (~120 days). Abnormal interdigital apoptosis during embryonic development: leading to fusion of fingers or toes. Reference: American Society for Surgery of the Hand 37 Summary 38  References Basic Concepts in Biomedical Sciences I. Lehninger Principles of Biochemistry 7th Edition. 39  MEDF1011 FOUNDATION COURSE FOR HEALTH SCIENCES I BOOST-UP SESSION (BUS) – PEER ASSISTED STUDY SESSION Objectives: To reinforce concepts you have learnt in the lecture through questions and discussions. You will learn the way to come up a conclusion for the problems encountering in specific lecture topics. Join BUS if you want to: Schedules: ❖ learn about critical thinking; Dates & Topics ❖ tackle unseen questions; ❖ perform better in the examination. Sept 27 (Fri) Format: Excitable Cell 12-15 students per group 5:30-6:15pm (enrollment required) and each Venue: to be confirmed group will be led by a BUS Leader. Each session lasts for 45 mins. Nov 8 (Fri) Cardiovascular system 5:30-6:15pm Venue: to be confirmed Enrollment: Available on Blackboard one week before each BUS session. If you have other engagement and turn out unable to join after enrollment, please contact Ms. Elaine Man ([email protected]) as soon as possible so that other students on the waiting list can join.