A Tour of the Cell AP Biology Fall 2015

Cells are necessarily small Most cells are between 1 and 100 micrometers They have to be that small to allow for intracellular communication and transport. cell size animation

If a cell is too big, the surface area to volume ratio is too low. The surface area is too small compared to the volume and the cell cannot take in enough to “feed” the center portion.

Prokaryotic Cells vs. Eukaryotic Cells: What unites us All cells have a plasma membrane (lipid bilayer) that surrounds the cell All cells have a cytosol which is a thick chemical soup (mostly water) in which everything inside of a cell floats. All cells have chromosomes (DNA) All cells have ribosomes (structures that carry out the process of producing proteins)

Prokaryotic Cells vs. Eukaryotic Cells: What separates us Prokaryotes have no membrane around the cell’s DNA. Eukaryotes have a nucleus that holds the DNA and the nucleus is surrounded with a nuclear membrane

Prokaryotic Cells vs. Eukaryotic Cells: What separates us Prokaryotes have no other membrane- bound organelles. Eukaryotes have many membrane bound organelles suspended in the cytoplasm. Prokaryotes are generally smaller. Eukaryotes are generally larger. Prokaryotes are only bacteria. Eukaryotes are never bacteria but comprise the other kingdoms

Prokaryotic Cells vs. Eukaryotic Cells: What separates us To sum up: 1. Prokaryotes are small and simple, lacking nuclear membranes as well as other membrane-bound organelles. 2.Eukaryotes are large and complex with a nuclear membrane and many other membrane-bound organelles

The Nucleus Function of the nucleus: contains most of the genes. –Nuclear envelope –Nuclear pores (holes in the nuclear envelope) –Chromosomes (DNA) –Nucleolus-makes RNA including ribosomes

Ribosomes Function – ribosomes carry out protein synthesis –Free ribosomes –Bound ribosomes

Endomembrane system Consists of many membrane organelles that are either in direct contact with each other or transfer vesicles to each other. Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles plasma membrane

Endoplasmic Reticulum (ER) 1.Rough –The ribosomes function to produce secretory proteins. (Also called glycoproteins) –Makes membranes 2.Smooth –Synthesis of lipids (steroids) –Metabolism of carbohydrates – detoxification of drugs and poisons (in liver cells)

Golgi Apparatus Has 2 “faces” cis face – receives vesicle from ER trans face – produces vesicles modification occurs between cis and trans faces. Vesicle also gets tagged destination.

Lysosomes Membrane-bound sac that the cell uses to digest macromolecules. Contains enzymes that can digest all major classes of macromolecules. These enzymes operate best at a low pH. The lysosome maintains that pH by constantly pumping H ions in. Phagocytosis – amoebas, white blood cells Autophagy – recycles cellular components. Ex: liver cells Programmed destruction – tadpoles, insect metamorphosis

Vacuoles Diverse Functions: –Food vacuole –Contractile vacuole –Central vacuole (tonoplast = membrane) Central vacuoles can hold: poisons, toxins, irritants, pigment, proteins, inorganic ions, water

Mitochondria Transforms energy in glucose to ATP in a process called cellular respiration. Mitochondria have their own ribosomes and their own DNA Called semiautonomous

Plastids Amyloplasts Chromoplasts Chloroplasts

Like mitochondria, chloroplasts have their own ribosomes and DNA and are also semiautonomous Chloroplasts are found only in plants and some protists – they convert solar energy sunlight into chemical energy and drive the synthesis of organic compounds.

Peroxisomes Compartments that contain enzymes that transfer hydrogen to oxygen Produce hydrogen peroxide as a by- product. Other enzymes (catalase, for example) break the hydrogen peroxide down. Transferring hydrogen work in breaking down fatty acids and detoxifying alcohol.

Plants vs. Animals Plant cells do not have: Lysosomes Centrioles Flagella (except some plant sperm) Animal cells do not have: Chloroplasts Central vacuole Tonoplast Cell wall plasmodesmata

Cytoskeleton A network of fibers in the cytoplasm. It’s major functions are: –organization –Mechanical support –Maintains shape –Anchorage for organelles The cytoskeleton is dynamic

Cell Surfaces and Junctions Plant Cells cell wall –protects the cell –maintains the shape of the cell –prevents excessive uptake of water What are cell walls made of??

Intercellular communication and connection Plants – Plasmodesmata – cell to cell communication in plants Animals – Tight junctions and demsosmes: fasten cells together Gap Junctions – provide cytoplasmic channels between adjacent cells (function just like plasmodesmata)