Looking at Cells n n Microscopes A basic

Looking at Cells n n Microscopes: A basic biology tool that allowed for the discovery of cells and cell parts. Simple microscope- hand lens Compound microscope- uses 2 or more lenses working together. The maximum useful magnification is 1200 -1500 x. Electron microscope- uses an electron beam in place of light. These can magnify over 500, 000 x or half a million times.

Electron Microscopes n SEM- scanning electron microscope- used to view surfaces like cell walls and cell membranes. n TEM-transmission electron microscopemore powerful- used to study tiny structures and organelles inside of cells. n STM-scanning-tunneling microscope is used to view the structure of large molecules.

Organelles n n n Organelle- a structure inside a cell that is surrounded by a membrane. Each organelle has a specific function or job. Membrane- covering around cells or organelles. They have several functions: 1. Membranes surround a cell or organelle and define its space. Separates living materials from the environment. 2. Membranes control materials that come and go from cells or organelles. 3. Serve to protect. 4. Membranes are made mostly of lipids.

2 Types of Cells Prokaryotes- Kingdoms Eubacteria and Archebacteria- all the bacteria, all the archebacteria and blue-green algae. The cells have no organelles & no nucleus. n All the cell chemistry is carried on in the cells cytoplasm. DNA floats in the cytoplasm in long strings or coils. n Eukaryotes: have internal membrane covered organelles. Also have a nucleus where DNA is found during most of the cells life. Kingdom Plantae, Animalia, Fungi and Protista are eukaryotes. n

Scientists of Cells n n n Robert Hooke- English- used microscope to view cork wood. Coined the term “cell”. Anton van Leeuwenhoek- Dutch- mid 1600’s, An eyeglass lense grinder who built microscopes and used them, The first scientist to describe living cells as seen through a simple microscope Robert Brown- first wrote about the cell nucleus. Rudolf Virchow first predicted that the nucleus contained genetic material and was responsible for cell reproduction. Matthias Schleiden- German, 1830’s, proposed that all plants were made of cells. Theodore Schwann- German, 1830’s, proposed that all animals are made of cells.

Cell Theory n Cell Theory- A cornerstone of modern biology! It has 3 Parts n 1. All living things are made of cells. n 2. The cell is the basic unit of life. n 3. All cells come from other living cells.

Hierarchy of organization in living things: n Cells Tissues Organ Systems Organism Cells of similar function combine to form tissues: nerve tissue, muscle tissue, meristem tissue in plants. n Two or more tissues form an organ: muscle, nerve and epithelial tissue form the heart. n Two or more organs form an organ system: stomach, liver, small intestine, teeth are parts of the digestive system. n An organism is several systems working together: a human and other vertebrates are made of 11 systems. n

Plasma Membrane n n The plasma membrane has several functions: 1. It surrounds the cell material and defines the cells space. 2. It separates the cell from the surrounding environment. 3. It controls the movement of materials into and out of the cell. This helps maintain a balanced living condition. (Homeostasis)

Plasma Membrane The plasma membrane is made of 2 layers of lipid with proteins inserted here and there. This is referred to as a “lipid bilayer”. The lipids also have phosphate groups attached so they are referred to as “phospholipids”. n The inserted proteins are sometimes known as transport proteins because they help move materials across the membrane. n

Membrane Crossing n Things that must cross the plasma membrane: n Water, oxygen, waste products, glucose, food, carbon dioxide are some things that must commonly cross the plasma membrane.

n Osmosis- the movement of water along a concentration gradient High concentration Equal concentration Low concentration

Fluid Mosaic Theory n n n The theory of the fluid mosaic model describes the structure of the plasma membrane and explains how and why it functions as it does. Each cell membrane is composed of 2 opposing layers of phospholipids. Each phospholipid molecule has a polar (water soluble) which is a phosphate. This is also called the hydrophilic or water loving end. The other end of the phospholipids is made of nonpolar (oil soluble) fatty acids. This is the hydrophobic or water hating end.

n These phospholipids in the membrane line themselves up with the polar phosphates facing outward toward the water soluble environment and facing inward toward the water soluble inside of the cell. n The nonpolar or hydrophobic ends of the phospholipids move into the middle of the membrane where there is no water. n Cholesterol molecules are found in between phospholipid molecules in the membrane. Cholesterol keeps the membrane liquid and allows the phospholipids molecules to move around.

Two Types of proteins Transport proteins are found sticking thru the plasma membrane and allow movement of particles across the membrane. 2 types: n 1. Channel proteins-these form openings that allow material dissolved in water to pass thru. This allows passive transport of sugars, amino acids and ions to cross the membrane. This simply forms an opening that allows these materials to move thru. n 2. Carrier protein- A protein molecule in the membrane that physically attaches to a molecule or particles and pulls or pushes it thru the membrane. A form of active transport. n

Eukaryotic Cell Structure n Cell walls: A solid covering around cells of plants, fungi, bacteria and some protests. No animal cells have cell walls. n It provides support and physical protection for the cell. It DOES NOT control movement of materials into or out of the cells. n Trees are able to grow to large heights because of the support given to their cells by cell walls. Plants cell walls contain cellulose as the main structural material.

Nucleus n n n Nucleus: A fairly large membrane covered organelle that controls the cell. It has several parts: all materials in the nucleus are referred to as nucleoplasm. 1. nuclear membrane or nuclear envelope surrounds the nuclear material and controls the movement of materials into the nucleus. 2. Chromatin- unwound DNA fibers inside the nucleus. The DNA contains the genetic code for all the cells proteins. During cell division, chromatin coils up into short spools called chromosomes. 3. Nucleolus- A small membrane covered area INSIDE the nucleus that builds ribosomes for the cells. Ribosomes build proteins for the cell.

Ribosomes n The sites of protein synthesis. n Makes proteins based on RNA instructions.

n Cytoplasm- a jelly like mixture of water, proteins, Chemicals, and organelles that make up all the cell except the nucleus. There are several organelles. n The clear fluid inside the cell.

ER 1. Endoplasmic reticulum- layers of manyfolded membranes that act as transport canals. These folded membranes act as sites for many chemical reactions. Many ribosomes are found on the ER, so lots of protein synthesis occurs there. n A folded membrane that forms a network of interconnected compartments in the cytoplasm n Smooth ER-areas with no ribosomes. n Rough ER- areas with ribosomes. n

Golgi bodies n Golgi bodies- similar in structure as the ER. These “package” protein molecules that must be excreted from the cell. This packaging allows the molecule to cross thru the cells plasma membrane. Golgi bodies are very numerous and active in cells that secrete proteins such as glands and digestive organs. n Closely stacked, flattened membrane sacs.

Vacuoles n Vacuoles- storage areas. Can store food, chemicals, starches, proteins, almost anything. Plant cell often have very large vacuoles. n A membrane-bound, fluid-filled sac. n Provides temporary storage of food, enzymes, and waste products

Lysosomes n Lysosomes- special vacuoles that breakdown or digest old, worn out organelles or food particles. n This allows the cell to recycle materials. n Digest excess or worn-out cell part, food particles, and invading viruses or bacteria

Mitochondria- found in all eukaryotic cells, these break down sugars and release energy. It has a highly folded inner membrane that serves as a “workbench” for enzymes. Cells that require a lot of energy will have many mitochondria. Liver cells may have 2500 each. n The structure of chloroplasts and mitochondria are very similar, but their function is directly opposite: chloroplasts build sugars, mitochondria break sugars apart. n

Endosymbiontic Theory Endosymbiontic theory- proposed in the 1960’s by Lynn Margulis (p. 392). The theory proposes that eukaryote cells evolved as a result of a symbiotic relationship between several types of prokaryote cells. n In other words, organelles such as chloroplasts and mitochondria were once free living prokaryotes, but became absorbed into a larger prokaryote to form a eukaryote cell. n

Cytoskeleton n n Cytoskeleton- a network of thin fibers that give support, shape and structure to a cell. There are 2 types of support materials: 1. microtubules that are thin, hollow protein tubes. 2. microfilaments that are thin, solid protein fibers. Imagine the cytoskeleton as the poles of a tent. It holds up the tent cover (plasma membrane) and provides space inside the tent.

Cell Wall n Firm, protective structure that gives the cell its shape in plants, fungi, most bacteria, and some protists.

Chloroplasts Chloroplast- found in plants, and some protests and some bacteria. This allows the cell to trap the energy in sunlight to power a food making process called photosynthesis. These contain the chemical chlorophyll which is a green pigment that actually traps the light energy. It has 2 major parts : n 1. The granum- which looks like stacks of coins surrounded by a membrane. Each “coin” is called a thylakoid. It is in the thylakoid that light energy is trapped. Grana n 2. The stroma- a fluid that surrounds the grana in the chloroplast. n

Locomotion n Flagella- a long tail like structure that is used as a “paddle” to move a cell thru water. A cell can have 1 or more of these. Cilia- a short hair like structure that is used as a locomotion device (movement). Usually a cell will have many of these. Some body cells in animals have cilia on their surface so that as the cilia move, particles can be moved around in the organism. Cilia cells in your respiratory system help move materials such as dust out of your lungs and into you throat. This helps keep the lung area clean.