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A Tour of the Cell Figures 4.8 – 4.16

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1 A Tour of the Cell Figures 4.8 – 4.16
CHAPTER 4 A Tour of the Cell Figures 4.8 – 4.16

2 Some functions of membrane proteins
Cytoplasm Fibers of extracellular matrix c Enzymatic activity b Cell signaling a Attachment to cytoskeleton and extracellular matrix e Intercellular joining f Cell-cell recognition d Transport Cytoplasm Cytoskeleton Figure 4.8

3 This behavior leads to the description of a membrane as a fluid mosaic
Membrane phospholipids and proteins can drift about in the plane of the membrane This behavior leads to the description of a membrane as a fluid mosaic Molecules can move freely within the membrane A diversity of proteins exists within the membrane

4 Selective Permeability
Membranes of the cell are selectively permeable They allow some substances to cross more easily than others They block passage of some substances altogether

5 The traffic of some substances can only occur through transport proteins
Glucose, for example, requires a transport protein to move it into the cell

The nucleus is the manager of the cell Genes in the nucleus store information necessary to produce proteins

7 Structure and Function of the Nucleus
The nucleus is bordered by a double membrane called the nuclear envelope It contains chromatin It contains a nucleolus

8 Ribosomes Chromatic Nucleolus Pore Nuclear envelope Figure 4.9

9 Ribosomes Ribosomes build all the cell’s proteins

10 How DNA Controls the Cell
DNA controls the cell by transferring its coded information into RNA DNA 1 Synthesis of mRNA in the nucleus mRNA The information in the RNA is used to make proteins Nucleus Cytoplasm 2 Movement of mRNA into cytoplasm via nuclear pore mRNA Ribosome 3 Synthesis of protein in the cytoplasm Protein Figure 4.10

Many of the membranous organelles in the cell belong to the endomembrane system

12 The Endoplasmic Reticulum
The endoplasmic reticulum (ER) Nuclear envelope Produces an enormous variety of molecules Is composed of smooth and rough ER Ribosomes Rough ER Smooth ER Figure 4.11

13 Rough ER The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

14 The functions of the rough ER include
Producing proteins Producing new membrane

15 After the rough ER synthesizes a molecule it packages the molecule into transport vesicles
4 Transport vesicle buds off Secretory protein inside transport vesicle Ribosome 3 Protein 1 Rough ER 2 Polypeptide Figure 4.12

16 Smooth ER The smooth ER lacks the surface ribosomes of ER and produces lipids, including steroids

17 The Golgi Apparatus The Golgi apparatus
Works in partnership with the ER Refines, stores, and distributes the products of cells Transport vesicle from ER “Receiving” side of Golgi apparatus Golgi apparatus New vesicle forming Transport vesicle from the Golgi “Shipping” side of Golgi apparatus Plasma membrane Figure 4.13

18 A lysosome is a membrane-enclosed sac
Lysosomes A lysosome is a membrane-enclosed sac It contains digestive enzymes The enzymes break down macromolecules

19 Lysosomes have several types of digestive functions
They fuse with food vacuoles to digest the food Lysosome Digestive enzymes Plasma membrane Digestion Food Food vacuole (a) Lysosome digesting food Figure 4.14a

20 They break down damaged organelles
Lysosome Digestion Damaged organelle (b) Lysosome breaking down damaged organelle Figure 4.14b

21 Vacuoles are membranous sacs
Two types are the contractile vacuoles of protists and the central vacuoles of plants Central vacuole Contractile vacuoles (a) Contractile vacuoles in a protist (b) Central vacuole in a plant cell Figure 4.15

22 A review of the endomembrane system
Rough ER Transport vesicle from ER Golgi apparatus Secretory vesicle from Golgi Secretory protein Vacuole Lysosome Plasma membrane Figure 4.16

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