Cells 2/2/2019. Cell Theory. Prokaryotic and Eukaryotic Cells. Life on Earth. Prokaryotic and Eukaryotic Cells. Bacterial Cell. Structure and Function

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1 Cell Theory Cells Structure and Function All living things are made of cells New cells come from pre-existing cells NO Spontaneous Generation Francesco Redi Italian 17 th century Louis Pasteur French 19 th century Antonie van Leeuwenhoek Made first sophisticated microscope Compound microscope visible light Electron microscope beams of electrons Proton microscope beams of protons Life on Earth All living things are made of one or more cells There are two major types of cells Prokaryotic cells Eukaryotic cells Plant cells Animal cells Prokaryotic and Eukaryotic Cells Prokaryotic cells have: DNA Cell wall and plasma membrane Cytoplasm and ribosomes Prokaryotic cells DO NOT have: A nucleus Compartmentalized specialized structures (organelles) Bacterial cells Bacterial Cell DNA cell membrane Cell wall Prokaryotic and Eukaryotic Cells Bacteria are prokaryotic cells and are generally much smaller than eukaryotic cells Some actually live inside the cells of a eukaryotic host 1

2 Prokaryotic and Eukaryotic Cells Cell Structure Eukaryotic cells include cells of Plants Protozoa and Algae Fungi Animals Eukaryotic cells have A plasma membrane Ribosomes DNA enclosed in a nucleus Compartmentalized specialized structures (organelles) All cells are enclosed by a structure called a plasma membrane The function of the plasma membrane is to control what enters and leaves the cell Cell Structure All membranes in a cell have similar structural components: phospholipids and proteins The phospholipids arrange themselves to form phospholipid bilayers with water both on the inside and the outside of the bilayer Cell Structure Since the phospholipids have two hydrophobic tails at one end and a hydrophilic head at the other end, they tend to gather in a specific arrangement Two layers with the hydrophilic heads pointing out and the hydrophobic tails on the inside. A Fluid Mosaic of Lipids and Proteins Because lipids and proteins can move about laterally within the membrane, the membrane is a fluid mosaic of lipids and proteins Fluid Mosaic Model 2

3 Fluid Mosaic Model Plasma Membrane Cell membranes are semipermeable Allow some things through but not others Water freely crosses the membranes This can be a problem If too much water enters the cell, it may swell or burst If too much water leaves the cell, it may shrink All organisms have ways of regulating how much water is in their cells. In most animals (except some simple marine invertebrates) the water content of tissues is regulated by the kidneys, so this isn t normally a problem. Fig. 3.7 Plasma Membrane Cell membranes are semipermeable Allow some things through but not others Gases such as oxygen and carbon dioxide pass freely But substances such as glucose and proteins require the help of the proteins in the cell membrane in order to enter the cell. Fig. 3.8 Transport Mechanisms Moving Materials in and out of Cells 3

4 Membrane Transport There are 4 main ways to transport small molecules into and out of a cell across the membrane Diffusion Osmosis Facilitated Diffusion Active Transport Diffusion Osmosis Beaker solution is hypotonic to bag Beaker solution is hypertonic to bag Beaker solution is isotonic to bag 4

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6 Fig Facilitated Transport Fig Fig Phagocytosis Active Transport Pinocytosis Receptor-mediated Endocytosis Fig Fig

7 Cell Wall Some cells (like plant cells and fungal cells) have a cell wall outside of the plasma membrane that give the cell structure and protect against water damage The cell wall is purely structural and has no control over what enters or leaves the cell Plant Cell Wall 7

8 Cytosol and Cytoplasm The cytoplasm is made up of the watery mixture inside the cell (called the cytosol) and the organelles The cytoplasm is contained by the plasma membrane. Organelles are membrane bound structures that carry out specific jobs for the cells. Cellular functions are more efficient when the work is compartmentalized in organelles. The nucleus is a membrane bound structure that encloses the DNA 8

9 Fig. 3.5 Endosymbiotic Theory for the origin of organelles in eukaryotic cells Endosymbiotic Theory for the origin of organelles in eukaryotic cells _ Endosymbiotic Theory Evidence Double membrane on chloroplast and mitochondrion Chloroplast and mitochondrion have bacterial DNA They undergo bacterial cell division in increase in numbers inside the cell Can make proteins from the genes on chromosome Chloroplast has same pigments as cyanobacteria 9

10 Mitochondria are organelles that carry out the process of aerobic respiration, which converts food energy to ATP, the type of energy a cell can use. Fig Page 61 Fig Chloroplasts are organelles found in plant cells. Chloroplasts can convert sunlight energy into chemical energy stored in the chemical bonds of glucose. 10

11 Lysosomes are small membrane sacs that contain digestive enzymes which break down food and other materials for the cell. Ribosomes are small structures that act like workbenches. Proteins are assembled at the ribosomes. Some ribosomes are free in the cytoplasm and some are bound to a structure called the endoplasmic reticulum. Cytoskeleton Some subcellular structures help cells divide and maintain their shape. Centrioles are involved in moving genetic material around when a cell divides 11

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13 How to Get Bigger Limit to how big a cell can be Depends on Surface Area to Volume Ratio How to get bigger? Be multicellular Each cell is small Has high SA/V ratio Cells can have specific functions Cells can work together to form TISSUES 13