Cell Structure and Function - williston.k12.sc.us

1 10/29/2014 1 Cell Structure and Function Chapter 6 Pg. 94 - 124 Cell Theory What is a cell? The basic functional unit of all living things. The Cell Theory All organisms are made of one or more cells . cells are the basic units of Structure and Function in living things. cells arise by division of pre-existing cells . Basically, cells come from other cells . Cytology Study of cells How do we do it? MICROSCOPES Light microscopes Electron microscopes Transmission electron microscope (TEM) Scanning electron microscope (SEM) Comparison of Scopes Light Microscope Electron Microscope Visible light passes through specimen and refracts light so specimen is magnified Focuses a beam of electrons through/onto specimen Magnifies up to 1000x Magnifies up to 1,000,000x Specimen can be alive/moving Specimen is non-living and in vacuum Color Black and white.

2 Colored by computer Can t see organelles other than nucleus Can see organelles Electron Microscope Comparison Transmission (TEM) Scanning (SEM) 2D 3D Internal cell structures Detailed surface structures Flat image with extreme detail Great field of depth Enhance contrast by staining atoms with heavy metal dyes Sample covered with thin film of gold, beam excites electrons on surface How do we Methods of studying cell Structure and Function : Cell fractionation: take apart cells and separate major organelles Ultracentrifuge: applies 1,000,000x force of gravity to separate cell organelles Most dense are at the bottom 10/29/2014 2 Importance of Cell Size As a cell grows, its volume increases faster than its surface area.

3 This makes the surface area-to-volume (SA/V) ratio DECREASE. So a larger cell has a smaller SA/V ratio. This can make chemical exchange difficult. cells must remain small to maintain a large SA/V ratio This allows exchange between the cell and the environment to occur the most efficiently Cell Types Prokaryotes (prokaryotic cells ) Domain Bacteria and Archaea Typically these cells only consist of a plasma membrane, DNA, ribosomes, cytoplasm, and often a cell wall Eukaryotes (eukaryotic cells ) Domain Eukarya Remaining organisms plants, animals, protists, fungi, etc.

4 Comparing Cell Types Prokaryotes Eukaryotes No nucleus Nucleus and nuclear envelope DNA stored in nucleoid DNA stored in nucleus No organelles other than ribosomes Many specialized membrane-bound organelles Small size Large size Primitive Complex Include bacteria and Archaea Include plants, animals, fungi, and protists Both have cytosol/cytoplasm, plasma membrane, ribosomes 10/29/2014 3 Organelles Cytoplasmic structures that separate metabolic reactions that occur within eukaryotic cells Chemical reactions are isolated and without interference or competition Many provide large surface area to maximize space for chemical reactions There are different concentrations of organelles in different cells .

5 Depending on their job Major Parts of the Cell Cell membrane Nucleus Ribosomes Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes Mitochondria Chloroplasts Microtubules, intermediate filaments, and microfilaments Flagella and cilia Centrioles and basal bodies Vacuoles and vesicles Extracellular structures Cell Membrane plasma membrane Separates internal metabolic events from the external environment Controls movement of materials into and out of the cell Consists of a phospholipid bilayer, or a double phospholipid membrane Nucleus Enclosed by a nuclear envelope two phospholipid bilayers Nuclear pores allow proteins and RNA molecules to exit the nucleus Nucleus contains DNA (genetic material) and acts as the control center of the cell DNA is typically in loose chromatin form, but condenses into rod-like chromosomes during cell division Also contains nucleolus (plural.)

6 Nucleoli), which synthesizes ribosomes Nuclear envelope attaches to rough endoplasmic reticulum membrane 10/29/2014 4 Ribosomes Makes proteins Large and small subunits Composed of rRNA and proteins Types: Free ribosomes float in the cytosol and produce proteins used within the cell Bound ribosomes are attached to the rough ER and make proteins for export from the cell Endoplasmic Reticulum (ER) Extend from the outer layer of the nuclear envelope Network of membranes and sacs Types Rough ER: ribosomes are present; creates glycoproteins, packages proteins for secretion, sends transport vesicles to Golgi, makes replacement membranes Smooth ER: no ribosomes.

7 Synthesis of lipids and steroid hormones, metabolizes carbs, stores calcium and helps regulate muscle contraction, breakdown of toxins, drugs, and toxic by-products from cellular reactions Golgi Apparatus ( Golgi body, Golgi complex) Group of cisternae (flattened sacs) arranged like a stack of bowls Collect and modify proteins and lipids made in other areas of the cell and package them into vesicles As modified proteins exit, they are packaged into a secretory vesicle that migrates to and merges with the plasma membrane, releasing its contents to the outside of the cell Other packaged substances may be retained within the cell for other purposes Lysosomes Vesicles from the Golgi apparatus that contain hydrolytic enzymes (enzymes that break down molecules by hydrolysis)

8 Breaks down food, cellular debris, and foreign invaders like bacteria Contribute to recycling cellular nutrients A low pH is favorable to the enzymes and is maintained inside the lysosome Any enzyme that might escape from the lysosome remains inactive in the neutral pH of the cytosol (so the cell will not be damaged by rupturing lysosomes) Only found in animal cells In the Real Lysosomal diseases are often fatal Digestive enzyme does not work in the lysosome, so biomolecules cannot be digested. Lysosome ends up with undigested material, growing larger and larger until it disrupts cell and organ Function .

9 More than 40 lysosomal storage diseases are known. Example: Tay-Sachs disease, a buildup of undigested fat in brain cells Lysosomes and Apoptosis Lysosomes can be used to kill cells when they are supposed to be destroyed, as in during development. Apoptosis: programmed cell destruction where lysosomes break open and kill the cell Example: tadpole tail, webbed fingers/toes Cancer cells override this Function to enable tumor growth. Typically apoptosis would be triggered in cells growing uncontrollably. 10/29/2014 5 Peroxisomes Break down various substances, including hydrogen peroxide (H2O2)

10 , fatty acids, and amino acids Common in liver and kidney cells , where they break down toxic substances In plant cells , peroxisomes modify by-products of photorespiration Mitochondria One large to thousands of smaller ones may be in a single cell The more activity a cell performs, the more mitochondria it will have Carry out aerobic cellular respiration Generates ATP in the presence of O2 Catabolic reaction Have 2 bilayer membranes Separates metabolic processes Inner membrane is folded to increase surface area, enhancing productivity The inner compartment, the mitochondrial matrix, is fluid-filled Chloroplasts Carry out photosynthesis Plant process of incorporating energy from sunlight into carbohydrates Contains chlorophyll (green pigment) for capturing solar energy Also have two membranes like the mitochondria Only found in plants Cytoskeleton Network of protein fibers extending from nucleus to plasma membrane in eukaryotic cells Several functions Structural support: maintains cell shape, anchors organelles Motility.