Cell Structure and Function Chapter 7 Biology Miller Levine

The Scientists…  Robert Hooke (1665) Viewed cork under a microscope Called the chambers he saw “cells”  Anton van Leeuwenhoek (1674) First to see living organisms in a drop of water

The Scientists…  Matthias Schleiden (1838) All plants are made of cells  Theodor Schwann (1839) All animals are made of cells  Rudolf Virchow (1855) All cells come from preexisting cells

The Cell Theory  All living things are composed of cells  Cells are the basic units of structure and function in living things  New cells are produced from existing cells

Unicellular vs. Multicellular  Unicellular – single-celled organism  Multicellular – many-celled organism Cell specialization – cells are specialized to perform certain functions Cells → Tissues → Organs → Organ systems → Organism

Prokaryotes vs. Eukaryotes  All cells have a cell membrane, cytosol, and ribosomes  Prokaryotes Do not have a nucleus or other membrane-bound organelles Ex. Bacteria such as E.coli  Eukaryotes Have a nucleus and organelles Ex. Plants, Animals, Fungi

Prokaryotes vs. Eukaryotes

Basic Cell Structures  Cell membrane – thin, flexible barrier around the cell; protects the cell Present in all cells  Cytoplasm – material inside the cell membrane (not including the nucleus) Present in all cells

Cell Wall  Found in many organisms, including plants, algae, fungi and nearly all prokaryotes  Not found in animal cells  Lies outside the cell membrane  Main function is to provide support & protection for the cell

Nucleus  All eukaryotic cells, including plants and animals have a nucleus  Prokaryotes do not have a nucleus  Controls most cell processes and contains the DNA

Nucleolus and Nuclear Envelope  Nucleolus: Inside the nucleus Where ribosomes are made  Nuclear Envelope: Double-membrane layer around the nucleus Allows material to move into and out of the nucleus

Nucleus

Cytoskeleton  Found in all eukaryotes but not prokaryotes  A network of protein filaments that helps the cell maintain its shape Microtubules – hollow tubes of protein that help maintain cell shape, are involved in cell division, aid in movement of organelles Microfilaments – long, thin fibers that function in the movement and support of the cell  It also is involved in cell movement

Ribosomes  Found in all cells  Main function is to make proteins  Can be found floating in the cytosol or attached to endoplasmic reticulum

Endoplasmic Reticulum (ER)  Found only in eukaryotic cells  Where components of the cell membrane are assembled  Two kinds: Smooth ER & Rough ER Smooth ER: no ribosomes; makes lipids; detoxifies harmful substances Rough ER: has ribosomes; involved in making proteins

Endoplasmic Reticulum

Golgi Apparatus  Found only in eukaryotic cells  Enzymes attach carbohydrates & lipids to proteins  Send proteins to their final destination in vesicles

Lysosomes  Found in animal cells only  Contain digestive enzymes  Break down lipids, carbohydrates & proteins from food into particles that can be used by the cell  Also break down “dead” organelles

Vacuoles  Not found in prokaryotes  Animal cells have small vacuoles  Plant cells have a large central vacuole  Store materials such as water, salts, proteins & carbohydrates

Chloroplasts  Found in all plant cells  Also found in some plant-like protists, such as algae  Use the energy from sunlight to make energy-rich food molecules during photosynthesis

Chloroplasts

Mitochondria  Found in eukaryotic cells only  Release energy from stored food molecules (cellular respiration)

Cilia and Flagella  Cilia Short, numerous projections that look like hairs Used for cell movement  Flagella Longer and less numerous than cilia  A cell usually has one or two flagella Used for cell movement

Plasma Membrane  Regulates what enters and leaves the cell (selectively permeable)  Provides protection and support  Phospholipid bilayer – two layers of phospholipids Proteins run through the layers Carbohydrates are attached to some of the proteins Fluid Mosaic Model

Cell Membrane

Diffusion  Molecules move from an area of high concentration to an area of low concentration  Movement continues until equilibrium is reached Molecules still move across the membrane, but there is no overall change  Many substances move across the membrane by diffusion  Does not require energy (passive transport)

Diffusion  An increase in any of the following will increase the rate of diffusion: Concentration Temperature Pressure

Diffusion

Osmosis  The diffusion of water Isotonic – equal concentration  Nothing happens Hypertonic – higher concentration of solute  Water moves out of the cell Hypotonic – lower concentration of solute  Water moves into the cell  No energy is required

Effects of Osmosis on Cells

Osmotic Pressure  In pure water, an animal cell would burst  Plant cells are protected by their cell wall  Some freshwater organism have special structures like contractile vacuoles to get rid of extra water

Facilitated Diffusion  Some molecules cannot cross the membrane without help  Some of the proteins in the membrane form protein channels  Materials still move from higher to lower concentrations  No energy is required

Facilitated Diffusion

Active Transport  Materials move from lower concentration to higher concentration  Requires an input of energy  Works kind of like a pump

Transport of Large Amounts  Endocytosis – movement into the cell Phagocytosis – “cell eating” – solid particles Pinocytosis – “cell drinking” – particles dissolved in water  Exocytosis – movement out of the cell

Phagocytosis

Pinocytosis