Cells

The Cell Theory Cells are the fundamental units of life. All organisms are composed of cells. All cells come from preexisting cells.

Cell Size Most cells are tiny, in order to maintain a good surface area-to-volume ratio. The volume of a cell determines its metabolic activity relative to time. The surface area of a cell determines the number of substances that can enter or leave the cell.

Cell Types Two types of cells: prokaryotic and eukaryotic Prokaryotes are without membrane-enclosed compartments. Eukaryotes have membrane-enclosed compartments called organelles, such as the nucleus.

Prokaryotic Cells Are enclosed by a plasma membrane Have DNA located in the nucleoid The rest of the cytoplasm consists of: Cytosol (water and dissolved material) and suspended particles Ribosomes—sites of protein synthesis

Prokaryotic Cells Some have a cell wall made of peptidoglycan. Some have a slimy capsule. Some have flagella made of flagellin for movement. A motor protein assists in actual movement.

Eukaryotic Cells Also have a plasma membrane and ribosomes. Have many other organelles that are membrane-bound.

Plasma Membrane Selectively permeable Made of phospholipids and proteins primarily Regulates what goes in and out

Ribosomes Site of protein synthesis In cytoplasm or on ER in eukaryotes Made of two units both rRNA

Nucleus Control center Contains the nucleolus (site of ribosome synthesis) Has nuclear pores to let out ribosomes and RNA

Rough ER Has ribosomes attached to begin protein synthesis. Newly made proteins enter the RER lumen. Once inside, proteins are chemically modified and tagged for delivery. The RER participates in the transport. All secreted proteins and most membrane proteins, including glycoproteins, pass through the RER.

Smooth ER More tubular, no ribosomes Chemically modifies small molecules such as drugs and pesticides. Site of glycogen degradation in animal cells. Site of synthesis of lipids and steroids.

Golgi Apparatus Composed of flattened sacs (cisternae) and small membrane-enclosed vesicles. 3 regions: cis, medial, trans Receives proteins from the RER—can further modify them Concentrates, packages, and sorts proteins Adds carbohydrates to proteins Site of polysaccharide synthesis in plant cells

Lysosomes Primary lysosomes- originate from the golgi; contain digestive enzymes for hydrolysis of polymers. Phagosome- originates from the plasma membrane; encloses food Secondary lysosomes- form when primary lysosomes fuse with phagosome for hydrolysis of polymers.

Mitochondria Site of aerobic cellular respiration. Parts of degraded glucose is converted into ATP. Contains an outer and an inner membrane (cristae). The inner fluid region is the mitochondrial matrix. Contains its own DNA and ribosomes. Divides through binary fission

Chloroplasts Type of plastid (site of photosynthesis) Found in plant cells and algae Contains the pigment chlorophyll for capturing light energy and converting it into chemical energy (glucose). Require CO2 and make O2 2 outer membranes with internal membranes that are stacked (thylakoids) Contains its own DNA and ribosomes. Divides through binary fission; each stack of thylakoids is called a granum.

Cell Wall Not on animal cells. Protection and support. Made of cellulose in plants.

Vacuoles Larger in plant cells compared to animal cells. Functions: storage, structure, digestion in plants Contractile vacuoles in protists help eliminate excess water.

Cytoskeleton Protein filaments 3 components Microfilaments (smallest)- movement of cell and parts; stabilize shape; made of actin Intermediate filaments- fixed positions; anchor organelles in relative locations; some made of keratin Microtubules (largest and longest)- form the cellular framework for motor proteins to move strutures in the cell; made of tubulin Cytoplasmic structures; Dynamic instability (microfilaments and microtubules; fast creation and break down); keratin found heavily in hair and fingernails; Cilia and flagella made of microtubules

Linking Cells Together Plant cells are connected by plasmodesmata (plasma membrane lined channels). Animal cells are connected by an extracellular matrix (collagen and proteoglycans).

Cell Junctions Gap junctions- allow substances to move from cell to cell Tight junctions- prevent movement of substances Desmosomes- hold cells together; materials can move within the matrix “Glue” cells together