The Life of a Cell Some history In 1665, Robert Hooke examined the bark of an oak tree under an early microscope. He thought he was looking at something similar to the small rooms of dormitories and prisons; hence the name: cells. Now, we know that Robert Hooke was not looking at living cells, but the remains of dead cell walls. Life is Based on the Existence of Cells The Cell Theory: Living things are made of cells. Cells are the basic unit of life. Cells come from preexisting cells. The study of cells is called cytology. Cells are diverse Even though cells are tiny, they are very complex! They vary in several ways: Size Shape Function (job) Cell Shape Why is there so much variety in cell shape? Shape relates to a cell s function. A flat shape of dead skin cells is well suited for covering the body surface. The long, thin, threadlike shape of nerve cells is well suited for transmitting messages throughout the body. Cell Size: Why are cells so small? 1. Volume increases faster than surface area. 2. Surface area is too small for cell to receive materials fast enough. 3. As a result, the cell divides 1
4 mm 4 mm 11/20/2014 Organisms are divided into TWO groups based on cell type: 1. Prokaryotic cells 2. Eukaryotic cells 4 mm 4 mm Surface Area = 96 mm 2 Volume = 64 mm 3 Ratio = 1.5 : 1 Surface Area = 192 mm 2 Volume = 64 mm 3 Ratio = 3: 1 Prokaryotic Cells Lack a nucleus and membrane-bound organelles. Unicellular. Fossils date to 3.5 billion years ago. Small, simple cells. All prokaryotes are bacteria. Eukaryotic Cells Have a nucleus and membrane-bound organelles. Some are unicellular, most are multicellular. Fossils date to 1.7 billion years ago. Large, highly organized cells. Plants, animals, protists and fungi are eukaryotes. Prokaryotes 2
What are prokaryotic cells? Unicellular organisms that lack a nucleus. Example of Prokaryotic Cells: Bacteria What do bacteria look like? PROKARYOTES In the space provided in your notes, write what you already know about bacteria. Bacillus: rod-shaped. Coccus: sphere-shaped. Archaebacteria ancient or extreme Eubacteria true or common Spirilus: spiral- or helicalshaped. Arrangement of Bacteria Where do bacteria live? Can be found on most materials and surfaces Billions on and in your body right now Organization of a Bacterial Cell ribosomes Nucleoid (DNA) E. Coli O157:H7 can make you very sick. This E. coli helps you digest food. Streptococcus can cause strep throat. Plasmid (DNA) Cell Wall 3
Some bacteria contain Flagella: used for movement Pilli: hair-like structures that anchor bacteria to a surface Capsule: outside layer that protect the bacteria from white blood cells. Some bacteria contain Endospore: Thick wall that encloses DNA Protects against harsh conditions (drought, harsh temperatures) 1) Asexually Binary fission Bacteria Reproduce 2) Sexually Conjugation Bacteria Reproduce Bacteria exchange plasmid DNA. How can bacteria be helpful? Bacteria play a large role in modern medicine, agriculture, and ecology. Decomposers break down organic material. Fermentation (bread, dairy, beer). Genetic engineering (GMOs and antibiotics). Take nitrogen in atmosphere and turn it into something organisms can use How can bacteria be harmful? Pathogens: Disease causing agents Bacteria cause disease by destroying living cells or by releasing chemicals that harm the body. Examples of sicknesses caused by bacteria: Strep throat Ear infections Lyme disease Tetanus Tuberculosis 4
Eukaryotes Why do cells have organelles? Division of labor into separate compartments (organelles) makes cell activities more ORGANIZED and EFFICIENT. This is made possible by the presence of LIPID membranes that form boundaries around each organelle (membrane-bound organelles). Nucleus Control center because it contains DNA Surrounded by the nuclear membrane Nuclear membrane has pores to allow things to enter/leave nucleus nucleus DNA Exists in Two Different Forms CHROMATIN Loose, uncoiled DNA. Stretched out so the cell can read the DNA. Present during the normal, everyday life of the cell. CHROMOSOMES DNA is tightly wound and organized Only during cell division Plasma (Cell) Membrane Boundary of cell (mostly lipids) Controls movement of materials in and out; maintains HOMEOSTASIS outside of cell Cell Wall Rigid outer layer of plant cells Made of cellulose Gives plant cells strength and support. Only in PLANT Cells inside of cell 5
Cytoplasm Jelly-like material that fills cell Chloroplast (a type of plastid) Present in LEAF cells Photosynthesis: Process of making food (glucose) Contain chlorophyll (green pigment) Plastids (only in PLANT cells) Store food or pigment molecules. cytoplasm chloroplasts chromoplasts in red pepper cells Leucoplasts in potato cells store starch Mitochondria The Powerhouse Breaks down food molecules (glucose) to release usable energy (ATP) Vacuole Fluid-filled storage area: Water Salts Enzymes Carbohydrates PLANT cells have one large vacuole; ANIMAL cells have several small ones. 6
Ribosomes Small, round organelles that produce proteins Can be scattered throughout the cytoplasm or bound to the Rough ER ribosomes Nucleolus Circular structure inside the nucleus Makes ribosomes Nucleus Nucleolus Endoplasmic Reticulum (ER) System of tubes and channels Rough ER has ribosomes for protein production Smooth ER produces lipids and also breaks down toxins rough ER smooth ER Golgi Apparatus Packaging factory for newly made lipids, proteins, and other molecules Vesicles - Small, circular packages that ship materials vesicles 7
Lysosome Contains DIGESTIVE ENZYMES to breakdown: a) food b) old cell parts c) waste d) invading viruses and bacteria e) the cell itself Cytoskeleton Network of protein fibers that provide structure and support to the cell. Anchors the organelles in the cytoplasm. cytoskeleton lysosomes Centrioles Pair of cylindrical structures that assist in cell reproduction (division) Only in ANIMAL cells Cilia and Flagella Cilia short hair-like extensions on the surface of some cells. Help move substances across the cell s surface. Flagella are longer than cilia and less numerous. Whip-like motion moves a cell from place to place. Plant Plant vs. Animal Cell Cell wall and cell membrane 1 large vacuole No centrioles Plastids Chloroplasts Square shape Animal Cell membrane only Several vacuoles Centrioles No plastids Variety of shapes (due to the flexible cell membrane) 8
9