Lecture Human anatomy and physiology - Chapter 3: Cells (part a)

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Chapter 3 - Cells: The living units (part a). Just as bricks and timbers are the structural units of a house, cells are the structural units of all living things, from one-celled “generalists” like amoebas to complex multicellular organisms such as humans, dogs, and trees. The human body has 50 to 100 trillion of these tiny building blocks. This chapter focuses on structures and functions shared by all cells.

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Nội dung Text: Lecture Human anatomy and physiology - Chapter 3: Cells (part a)

Cells: The Living Units
 The cell is the smallest structural and functional living unit  Organismal functions depend on individual and collective cell functions  Biochemical activities of cells are dictated by their specific sub cellular structures called organelles
 Over 200 different types of human cells  Types differ in size, shape, subcellular components, and functions
Erythrocytes Fibroblasts Epithelial cells (a) Cells that connect body parts, Nerve cell form linings, or transport gases Skeletal (e) Cell that gathers information Smooth Muscle and control body functions muscle cells cell (b) Cells that move organs and Sperm body parts Macrophage (f) Cell of reproduction Fat cell (c) Cell that stores (d) Cell that nutrients fights disease Copyright © 2010 Pearson Education, Inc. Figure 3.1
 All cells have some common structures and functions  Human cells have four basic parts: ◦Plasma membrane flexible outer boundary ◦Cytoplasm intracellular fluid ◦Organelles multiple functions ◦Nucleus control center
Chromatin Nuclear envelope Nucleolus Nucleus Smooth endoplasmic reticulum Plasma Mitochondrion membrane Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being Cytoskeletal released from cell elements by exocytosis • Microtubule • Intermediate filaments Peroxisome Copyright © 2010 Pearson Education, Inc. Figure 3.2
 Bimolecular layer of lipids and proteins in a constantly changing fluid mosaic  Plays a dynamic role in cellular activity  Separates intracellular fluid (ICF) from extracellular fluid (ECF) ◦Interstitial fluid (IF) = ECF that surrounds cells
Extracellular fluid (watery environment) Polar head of Cholesterol phospholipid Glycolipid molecule Glycoprotein Carbohydrate of glycocalyx Outward- Integral facing proteins layer of Filament of phospholipids cytoskeleton Inward-facing Bimolecular Peripheral layer of lipid layer proteins phospholipids containing Nonpolar proteins tail of phospholipid Cytoplasm molecule (watery environment) Copyright © 2010 Pearson Education, Inc. Figure 3.3
 Phospholipids (lipid bilayer) ◦Phosphate heads: polar and hydrophilic ◦Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b)
1. Transport 2. Receptors for signal transduction 3. Attachment to cytoskeleton and extracellular matrix
(a) Transport A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane. Copyright © 2010 Pearson Education, Inc. Figure 3.4a
(b) Receptors for signal transduction Signal A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. Receptor Copyright © 2010 Pearson Education, Inc. Figure 3.4b
(c) Attachment to the cytoskeleton and extracellular matrix (ECM) Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together. Copyright © 2010 Pearson Education, Inc. Figure 3.4c
4. Enzymatic activity 5. Intercellular joining 6. Cellcell recognition
(d) Enzymatic activity Enzymes A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here. Copyright © 2010 Pearson Education, Inc. Figure 3.4d
(e) Intercellular joining Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. CAMs Copyright © 2010 Pearson Education, Inc. Figure 3.4e
(f) Cell-cell recognition Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells. Glycoprotein Copyright © 2010 Pearson Education, Inc. Figure 3.4f
 Plasma membranes are selectively permeable  Some molecules easily pass through the membrane; others do not
 Passive processes ◦No cellular energy (ATP) required ◦Substance moves down its concentration gradient  Active processes ◦Energy (ATP) required ◦Occurs only in living cell membranes
 What determines whether or not a substance can passively permeate a membrane? 1. Lipid solubility of substance 2. Channels of appropriate size 3. Carrier proteins PLAY Animation: Membrane Permeability