Chapter 7: Cell Structure and Function

1665 Robert Hooke used an early compound microscope to look at a thin slice of cork

He saw thousands of tiny chambers he called "cells"

Today we know that cells are not empty. They contain living matter

Anton van Leeuwenhoek observed pond water and other things. The microscope revealed a world of tiny living organisms.

Matthias Schleiden- Botanist that said all plants are made of cells

Theodor Schwann- Biologist that said all animals are made of cells

Rudolf Virchow- Said cells come from other cells

All of these scientists developed the Cell Theory

1. All living things are made of cells

2. Cells are the basic units of structure and function in living things

3. Cells come from other cells

Compound Light Microscope- like we use in lab

Electron Microscopes: 1000X stronger

1. Transmission Electron Microscope (TEM)- Used to look at thin slices of tissue

2. Scanning Electron Microscope (SEM)- Used to look at the surface of objects and organisms. Gives 3-D image.

Cells are a variety of sizes and shapes. But all cells have two things in common:

 1) surrounded by cell membrane

 2) contain DNA

Two kinds of cells:

1) Prokaryotic- Do NOT have a true nucleus or membrane bound organelles

 PRO= before

2) Eukaryotic- DO have a true nucleus and membrane bound organelles

 EU= true

Prokaryotic Cells

Bacteria are prokaryotic

Eukaryotic Cells

Usually larger and more complex than prokaryotic cells.

Great variety of types. Unicellular organisms and multicellular organisms.

Plants, Animals, Fungi and Protists

A eukaryotic cell is similar to a factory.

They have many parts called organelles that have particular jobs.

There are two main parts (areas)

 1) cytoplasm (part outside nucleus)

 2) nucleus

Nucleus

The main office

· The control center of the cell

· Contains DNA which has instructions for making proteins and other molecules

· Surrounded by nuclear envelope (membrane with two layers) that has holes in it called nuclear pores which allow things into and out of the nucleus.

· Chromatin is found in the nucleus. It forms Chromosomes during cell division

· Nucleolus is an area in the nucleus where ribosomes are made

Ribosomes

Machine in factory

· Small particles of RNA where proteins are made using a recipe from DNA in the nucleus (the boss)

· Found in the cytoplasm and attached to Rough Endoplasmic Reticulum

Endoplasmic Reticulum

Assembly Line in factory

· Where lipids and proteins are made

· Rough ER has ribosomes on it and makes protein that goes into ER and is changed and repackaged

· Smooth ER does not have ribosomes. It makes lipids and detoxifies the body

Golgi Apparatus

Customization Shop

· Modifies, sorts, and packages proteins that come from the ER for storage or export from the cell

· Ship proteins to their final destination in the cell or outside the cell

Lysosomes

Cleanup Crew

· Small organelles filled with enzymes

· Breakdown lipids, carbohydrates, and proteins into small molecules that can be used by the cell

· Breakdown worn out parts and "junk" in cell

· Tay-Sachs is a disease that has been traced to lysosomes that fail to function correctly

Vacuoles

Storage Containers

· Saclike structure for storage of water, salts, proteins, and carbohydrates

· Some cells like plant cells have one large vacuole to store liquid

· Some unicellular organisms have a contractile vacuole which pumps excess water out of the cell to maintain homeostasis

Mitochondria

Powerhouse of the cell

· Convert chemical energy stored in food into compounds that the cell can use

· Enclosed by two membranes

· In humans, nearly all mitochondria come from the egg (mom)

· Contain their own DNA

Chloroplasts

Solar power plants

· Found in plants

· Capture energy from sunlight and convert it into chemical energy through process called photosynthesis

· Surrounded by two membranes

· Inside are stacks of membranes which contain the green pigment chlorophyll

· Contain their own DNA

Cytoskeleton

Support for building

· Internal supporting structure

· Network of protein filaments that helps cell maintain its shape

· Involved in movement

· Made of two protein filaments called microfilaments and microtubules

Microfilaments

· Threadlike structures made of protein

· Form network of support and flexible framework in cell

· Help some cells move (amoeba)

Microtubules

· Hollow structures made of protein

· Maintain cell shape

· Important in cell division (form spindle fibers which pull chromosomes apart)

· Form Centrioles in animal cells

· Form cilia and flagella to help some cells swim

Cell Membrane

· Thin flexible barrier often called a "fluid mosaic model"

· Regulates what enters and leaves the cell

· Provides protection and support

· made of a double-layered sheet called a lipid bilayer

· Has proteins embedded in it which act like doorways

· Carbohydrates are attached to the proteins which act like identification cards and help cells communicate

Cell Wall

· Found outside cell membrane of plants, algae, fungi and many prokaryotes

· Provides support and protection for cell

· Made of carbohydrate and protein

· Plant cell walls are made mainly of cellulose

Diffusion

· Particles in a solution move constantly

· Particles tend to move from an area of high concentration to low concentration

· When concentration is equal everywhere, it has reached equilibrium

· Substances diffuse across membranes without requiring the cell to use energy (passive transport)

Osmosis

· If a substance can diffuse across a membrane, the membrane is said to be permeable to it and impermeable if it can't diffuse across it

· Water diffuses easily

· Osmosis is the diffusion of water across a selectively permeable membrane from an area of high concentration to low concentration

· Semipermeable- When a membrane allows some things to diffuse through it and does not allow other things to diffuse

· Water will tend to move across the membrane until equilibrium is reached

· If a solution has equal amounts of solvent and solute on each side of a membrane, the solution is Isotonic.

· Hypertonic- more solute than solvent

·  If a cell is put in a hypertonic solution, the cell will SHRINK

· Hypotonic- less solute than solvent  If a cell is put in a hypotonic solution, the  cell will SWELL

· Cells of large organisms don't usually come in contact with fresh water. Blood is isotonic.

· Bacteria and Plant cells do come in contact with fresh water but have cell walls to protect them from expanding and bursting.

Facilitated Diffusion: Cell membranes have protein channels that act like carriers, making it easier for certain molecules to cross. They "facilitate" the diffusion of molecules.

There are hundreds of different channels that only allow certain molecules to come through.

It will only occur if there is a higher concentration on one side of the membrane. It doesn't require energy. It's passive transport.

Active Transport: Cells sometimes have to move substances in the opposite direction than they want to go. This requires energy and is called active transport.

It's usually done by transport proteins called "pumps" in the membrane.

Calcium, potassium and sodium ions are moved across the membrane this way.

Endocytosis: Movement of substances into a cell

 1) Phagocytosis: movement of solids  into cell

 2) Pinocytosis: movement of liquids into cell

Exocytosis: Movement of substances out of a cell

Unicellular Organisms: One celled organisms. They react and behave the same as multicellular organisms.

Multicellular Organisms: Have more than one cell. Great variety of organisms. Cells within that organism are specialized to divide up the work that needs to be done within that organism.

 RBC- transport oxygen

 Pancreas cells- produce enzymes to   digest food

 Muscle cells- allow us to move

Many cells make tissues

Many tissues make organs

Many organs make organ systems