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2 Chapter 3 Cell Structure

3 Introduction The cell is the basic unit of biological organization Basic composition –Protoplasm –Cell membrane –Organelles Eukaryotic vs. prokaryotic

4 History of the Cell Theory

5 Proposed in 1830s by Schleiden and Schwann Modern cell theory –Cells are the smallest complete living things –All organisms are composed of one or more cells –Cells arise only from other cells –All existing cells are descendants of the first cells

6 Anatomy of a Typical Eukaryotic Cell

7 The Cell Membrane Double phospholipid layer with embedded proteins Membrane transport: selectively permeable membrane –Osmosis –Protein channels –Active transport –Fluid mosaic model

8 The Cell Membrane

9 Cytoplasm of the Cell Mostly water with chemical compounds in solution or colloid –Solution vs. colloid Individual vs. clumped atoms or ions distributed in medium Polar compounds go into solution Nonpolar compounds go into colloidal suspension

10 The Nucleus Control center of the cell Nuclear membrane has pores to allow the passage of substances Chromatin genetic material inside nucleoplasm Nucleolus: site of ribosome formation

11 The Mitochondria Powerhouses of the cell Cristae: inner folds where cellular respiration occurs Energy requirements of cell determine cristae number

12 Lysosomes Digestive enzyme packages Function –Digest stored food –Maintenance and repair of organelles –Suicide agents for old or weak cells

13 Endoplasmic Reticulum System of membranes that makes up channels Connects with outer nuclear and cell membranes Cisternae: sac like or channel like cavities

14 Endoplasmic Reticulum (cont’d.) Rough ER –For protein synthesis –Attached ribosomes Smooth ER –Fat transport –Sex hormone synthesis

15 Endoplasmic Reticulum (cont’d.) Golgi apparatus –Collection of flat saclike cisternae –Concentration and collection of cellular compounds –Storage warehouses of the cell –Carbohydrate synthesis site

16 Ribosomes Distributed throughout cytoplasm Attached to rough endoplasmic reticulum No membrane covering Site of protein synthesis

17 Ribosomes (cont’d.) Protein functions –Structure, enzymes or catalysts, immune response DNA contains the code for a particular protein –DNA found in nucleus

18 Ribosomes (cont’d.) Transcription –Messenger RNA copies DNA code and leaves nucleus Translation –Transfer RNA picks up amino acids –Ribosomes link amino acids together

19 Ribosomes (cont’d.)

20 Centrioles Centrosome: two centrioles at right angles to each other –Composed of nine sets of triplet fibers Form spindle fibers during cell division Guide duplicated chromosomes to daughter cells

21 Cilia and Flagella Hairlike protrusions from cell membrane Nine double fibrils around two single central fibrils Cilia move materials across cell surface Flagellum propels cell through a medium

22 Plastids of Plant Cells Chloroplasts –Most common plastid –Photosynthesis: conversion of light into chemical energy –Granum Made of thylakoids Connected by lamella Chromoplasts: carotenoid pigments Leucoplasts: store food

23 Plastids of Plant Cells (cont’d.) Cell membrane surrounded by cell wall Cell wall composed of cellulose –Cellulose Dietary fiber Synthesized by Golgi bodies Animal cells do not have cell walls

24 Summary Discussed the modern cell theory and its origins Discussed the different parts of eukaryotic cells including the cell membrane, cytoplasm, and organelles Discussed protein synthesis Described some of the differences between plant and animal cells