Organization of the Cell

Cell theory Cells are the basic living units of organization and function All cells come from other cells Work of Schleiden, Schwann, and Virchow contributed to this theory Each cell is a microcosm of life

Cell organization and size permit homeostasis Homeostasis: The balanced internal environment of the body; the automatic tendency of an organism to maintain such a steady state.

Cell surface area-to-volume ratio Plasma membrane must be large enough relative to cell volume to regulate passage of materials

Organization is basically the same in all cells All cells have a plasma membrane, which is a selective barrier Cells have internal organelles that are specialized for various functions Cell size is limited by the surface to volume ratio, so cells remain small Cell shape and size are related to function.

Surface to volume ratio As the cell size increases, the volume becomes too large for the surface membrane to handle.

Cell surface area-to-volume ratio

Biological size and cell diversity

Small size… (add) Molecules must be transported to the locations where they are converted into other forms With small cell size, distances molecules travel within them are relatively short which speeds up many cellular activities

Cells are studied by a combination of methods Robert Hooke: identified the cell walls and gave the structure the name “cell”. Study of the cell was not possible until microscopes.

Microscopes Light microscope, referred to as compound microscope, used by most students Two features determine how clearly an object is viewed Magnification: how much larger Resolution: how clear Light microscope has 500 times more resolution than human eye

Allows study of the ultrastructure of cells Electron microscope Developed in the 1950s Allows study of the ultrastructure of cells 10,000 times more resolution than human eye

Types of electron microscope Transmission electron microscope: used for studying ultra structure. Specimen must be specially prepared and sliced very thin. Scanning electron microscope: bounces electrons off a thin metallic coating on the object. Enables surface area to be viewed.

Comparing light and electron microscopy

Cell fractionation Used to determine function of organelles Cells broken apart and the resulting cell extract spun in a centrifuge Centrifugal force separates extract Pellet: solid particle Supernatant: fluid material

Cell fractionation

Types of Cells http://www. tvdsb. on Prokaryotic Cells: Bacteria and Archea 1. lack membrane bound organelles 2. smaller in size than eukaryotes 3. DNA is located in nucleoid area and is not bound by a nuclear membrane 4. Most have cell walls 5. Have ribosomes and storage granules

Eukaryotic cells: all other organisms 1. nucleoplasm: contains chromosomes which package DNA 2. cytoplasm: area outside the nucleus; contains cytosol and organelles, many of which are membrane-bound 3. type of cell determines which organelles are present and in what numbers

Divide cell into compartments, allowing for specialized activities Functions of cell membranes Divide cell into compartments, allowing for specialized activities Interacting membranes form endomembrane system Vesicles transport materials between compartments

Diagram of a plant cell

Diagram of an animal cell

The cell nucleus Contains DNA Bounded by Nuclear envelope Double membrane perforated with nuclear pores DNA forms chromatin, which is organized into chromosomes Nucleolus RNA synthesis and ribosome assembly

The cell nucleus

Endoplasmic reticulum (ER) Network of folded internal membranes in the cytosol Smooth ER Site of lipid synthesis Site of detoxifying enzymes Rough ER Ribosomes manufacture proteins Proteins may be moved into the ER lumen

Endoplasmic reticulum (ER)

Glycoproteins transported to the cis face Golgi complex Cisternae that process, sort, and modify proteins In animal cells, Golgi complex also manufactures lysosomes Glycoproteins transported to the cis face Golgi modifies carbohydrates and lipids and packages into vesicles; which then may leave the cell

Golgi complex

Lysosomes break down worn-out cell structures, bacteria, and other substances Primary lysosomes bud from the Golgi complex Secondary lysosomes form by fusion of a primary lysosome with a vesicle containing ingested material Involved in apoptosis (programmed cell death)

Lysosomes

Peroxisomes metabolize small organic compounds Transfer hydrogen from various compounds to oxygen, forming hydrogen peroxide Catalase is an enzyme that breaks down hydrogen peroxide Most common in cells that synthesize, store, and degrade lipids

Peroxisomes and lysosomes

Vacuoles Large, fluid-filled sacs with a variety of functions. May function in storage of toxins or pigments Plant vacuoles are typically large and allow the cell to increase in size Protist vacuoles may involve digestion or excretion.

Mitochondria Sites of aerobic respiration Organelles enclosed by a double membrane Cristae and matrix contain enzymes for aerobic respiration Nutrients broken down and energy packaged in ATP Carbon dioxide and water by-products

Mitochondria

Chloroplasts Plastids that carry out photosynthesis Inner membrane of chloroplast encloses the stroma During photosynthesis, chlorophyll traps light energy Energy converted to chemical energy in ATP; sugars/food for the plant are manufactured.

Chloroplast

Cellular respiration and photosynthesis

Equation for photosynthesis 6H2O + 6CO2  C6H12O6 + 6 O2 If you turn the arrow around, you have the equation for cellular respiration.

Internal framework made of Cytoskeleton Internal framework made of Microtubules Microfilaments Intermediate filaments Provides structural support Involved with transport of materials in the cell

The Cytoskeleton

Cilia and flagella Thin, movable structures that project from cell surface Function in movement Microtubles anchored in cell by basal body

Structure of cilia

Cilia and flagella

Glycocalyx, cell coat formed by polysaccarides extending from plasma membrane Many animal cells also surrounded by an extracellular matrix (ECM) Most bacteria, fungi, and plant cell walls made of carbohydrates

Extracellular matrix

Plant cell walls