Structure & Function of Cells

Transcription

1 Anatomy & Physiology Unit 4 Structure & Function of Cells Paul Anderson 2011

2 Anatomy of a Generalised Cell Attached or bound ribosomes Cilia Cytosol Centriole Mitochondrion Rough endoplasmic reticulum Nuclear envelope surrounding nucleus Nuclear pores Fixed ribosomes Secretory vesicles Microvilli Lysosome Smooth endoplasmic reticulum Cytoskeleton Cell membrane Golgi apparatus Free ribosomes Nucleoplasm Nucleolus Chromatin Martini & Bartholomew, fig 3-2

3 CELL ORGANELLES LYSOSOME Digestive Organelle

4 THE LYSOSOME DIGESTION of POLYMERS AUTOPHAGY AUTOLYSIS

5 CELL ORGANELLES Large subunit Free Ribosomes Small subunit RIBOSOMES Protein Factories Attached (Bound) Ribosomes

6 CELL ORGANELLES ROUGH ENDOPLASMIC RETICULUM

7 CELL ORGANELLES SMOOTH ENDOPLASMIC RETICULUM

8 CELL ORGANELLES GOLGI BODY (APPARATUS) Packaging Center

9 THE GOLGI BODY (APPARATUS) Endoplasmic reticulum Forming face Maturing face Cytosol Lysosomes Extracellular Fluid Cell membrane Secretory vesicles Exocytosis Transport vesicle Golgi Apparatus Membrane renewal vesicles Martini & Bartholomew, fig 3-14 Vesicle incorporation in cell membrane

10 THE ENDOMEMBRANE SYSTEM -1 also includes Cell (Plasma) Membrane Nuclear Envelope and Vacuoles

11 THE ENDOMEMBRANE SYSTEM -2 Nucleus Rough ER Golgi Apparatus Smooth ER Nuclear envelope Transport vesicle Secretion vesicle Exocytosis Lysosome cell membrane

12 The Endomembrane System -3 Rough Endoplasmic Reticulum Nuclear Envelope Transport Vesicles received by Lysosome Golgi Body Secretion Vesicles SmoothEndoplasmic Reticulum

13 CELL ORGANELLES CHROMATIN

14 CELL ORGANELLES NUCLEOLUS

15 THE NUCLEUS = DNA (GENES) + PROTEIN (histone) Transcription Translation GENETIC LIBRARY - NUCLEUS has all the GENES CONTROL CENTER for CELL S PROTEINS

16 CELL ORGANELLES MITOCHONDRION Cell s Powerhouse Self replicating powerhouse of aerobic cells: forms most of aerobic cell s ATP by aerobic respiration. Organic molecules are oxidised by dehydrogenation reactions (Krebs or TCA Cycle) in matrix, forming CO 2.. ATP is generated on inner membrane (cristae) by oxidative phosphorylation via an electron transport chain (cytochromes) which passes H 2 to O 2 forming metabolic H 2 O.

17 MITOCHONDRION Structure & Functions Organic molecules O 2 CO 2 ATP Matrix Cristae Martini & Bartholomew, fig 3-15 Electron Transport Chain

18 MITOCHONDRION Aerobic Respiration C 6 H 12 O 6 + 6O > 6CO 2 + 6H 2 O + ENERGY > ATP GLUCOSE GLYCOLYSIS 6CO 2 2 PYRUVIC ACIDS ATP OXDATIVE PHOSPHORYLATION 6H 2 O O 2 KREBS (TCA) CYCLE Matrix Cristae O2 O 2 Electron Transport Chain

19 CELL ORGANELLES MICROVILLI Extensions of cell membrane which increase surface area in absorptive cells, e.g. small intestine CELL (PLASMA) MEMBRANE

20 THE CELL (PLASMA) MEMBRANE The cell membrane consists mainly of LIPIDS and globular PROTEINS. MEMBRANE LIPIDS are mostly PHOSPHOLIPIDS which form a double layer (bilayer) in the membrane. Most MEMBRANE PROTEINS are mobile and embedded in the fluid lipid bilayer as integral proteins which span the membrane. Some proteins (peripheral proteins) are on the surface only. Animal cells have a carbohydrate CELL COAT (GLYCOCALYX) on the outer membrane surface composed of small Polysaccharides. The GLYCOCALYX functions as a chemical identity marker for cell recognition Hydrophilic region Hydrophobic region Hydrophilic region Phospholipids Glycocalyx ICF Campbell & Reece fig 7.3 Proteins ECF Structure of the Cell Membrane

21 FUNCTIONS OF MEMBRANE LIPIDS The PHOSPHOLIPID BILAYER creates a hydrophobic interior to the membrane which allows free diffusion of other hydrophobic (lipid - soluble) molecules (e.g. O 2, CO 2, lipids) but blocks passage of hydrophilic (charged) molecules or ions (e.g. H 2 O, Na +, K +, amino acids, glucose) The fluidity of the membrane is maintained by unsaturated Phospholipid tails and by Cholesterol. Fluid membrane Unsaturated tails of phospholipids Less fluid membrane Cholesterol within cell membrane Campbell & Reece fig 7.5

22 Transport Functions of Membrane Proteins -1 MEMBRANE PROTEINS have 3 important transport functions. Some membrane proteins have HYDROPHILIC PORES (CHANNELS) which allow free diffusion of small hydrophilic molecules or ions (e.g.na +, K + Cl - and H 2 O). Some membrane proteins act as CARRIERS for hydrophilic molecules or ions (e.g. glucose, amino acids, Na + and K +). Campbell & Reece fig 7.8

23 Transport Functions of Membrane Proteins -2 Some membrane proteins act as RECEPTORS for molecules arriving at the cell. signal molecule Signal molecules such as many Hormones (e.g. insulin) and some Neurotransmitters must combine with a specific receptor protein to cause an effect on the target cell. Some large biomolecules entering the cell by Endocytosis (e.g. cholesterol) must first combine with a receptor protein. protein

24 Cell Membrane Structure EXTRACELLULAR FLUID Carbohydrate chains Phospholipid Protein bilayer with channel Hydrophobic tails Proteins Cell membrane Protein with gated channel Cholesterol CYTOPLASM Proteins Hydrophilic heads Cytoskeleton Martini & Bartholomew, fig 3-3

25 Summary of Membrane Structure & Function GLYCOCALYX (CELL COAT) outside of membrane: composed of small Polysaccharides: functions in cell recognition. HYDROPHILIC SURFACE Charged heads of phospholipids orient PLs in the membrane HYDROPHOBIC INTERIOR Bilayer of PL hydrocarbon tails Blocks passage of hydrophilic mols/ions EXTRACELLULAR SIDE OF MEMBRANE Microfilaments of cytoskeleton MEMBRANE PROTEINS channels (pores) Integral proteins help Cholesterol transport hydrophilic mols/ions by acting as carriers or by having hydrophilic channels Peripheral (pores) or by proteins acting as receptors Cholesterol Integral protein HYDROPHOBIC TAILS HYDROPHILIC HEADS PHOSPHOLIPID BILAYER CYTOPLASMIC SIDE OF MEMBRANE

26 SUMMARY OF MEMBRANE FUNCTIONS SEGREGATES cell & organelles into chemical compartments. SELECTIVE BARRIER, controlling the flow of molecular traffic between the ICF and the ECF (e.g. membrane lipids, protein carriers, membrane pores). Intracellular and Intercellular COMMUNICATION (e.g. nerve impulses, secretion and reception of hormones and neurotransmitters). VESICLE formation and reception in endo and exocytosis. ANCHORAGE of cells (e.g. via cell junctions).

27 The EXTRACELLULAR MATRIX The ECF of animal tissues contains secreted GLYCOPROTEIN fibers attached to the membrane. The combination of ECF and fibers form the extracellular MATRIX of connective tissues Collagen fiber The protein COLLAGEN gives strength to the matrix. ECF EXTRACELLULAR MATRIX CYTOPLASM Glycoproteins In the matrix Other glycoproteins attach to membrane proteins and influence the cell s functions via the cytoskeleton.