Cellular Biology Cells: theory, types, form & function, evolution
The Cell Theory Problems with the Cell Theory? The cell theory has three components: 1. all living organisms are made up of one or more cells 2. the cell is the fundamental unit of life 3. all cells arise from other pre-existing cells
So what is a cell? A cell is The most basic unit of any organism The smallest unit of life that can perform all the necessary functions of life A three-dimensional structure where the essential chemical reactions of life take place All cells have: plasma membrane encompasses the cell cytoplasm the jelly-like fluid that fills the inside of the cell ribosomes cellular structures where proteins are made nucleic acids: May be used for: Information storage (ex. DNA) Energy storage molecules (ex. ATP) Only two kinds of cells prokaryotic: eukaryotic pro = before, preceding karyo = kernel, nucleus eu = true
Characteristics of prokaryotic cells Prokaryotic Cells: have no nucleus have no membrane-bound organelles contain DNA which is circular have a rigid cell wall may have pili &/or flagellum consist of only single celled organisms bacteria & archaea
Characteristics of eukaryotic cells Eukaryotic Cells large & complex have a membrane bound nucleus & other membrane bound organelles with specific functions have DNA in a linear format Can form single celled organisms Protists multicellular organisms animals, plants & fungi
Types & Characteristics of Eukaryotic Cells Animal cells Plant cells
Types & Characteristics of Eukaryotic Cells Fungus Cell Protist Cell
Questions: How are eukaryotic and prokaryotic cells related? How are they different?
Cell parts: plasma membrane Structure: Made of a phospholipid bilayer polar/non-polar regions that are hydrophilic & hydrophobic Functions: Separates the inside of the cell (cytoplasm) from outside environment Selectively permeable: controls what molecules move into or out of the cell Other functions see membrane proteins!
Embedded molecules of the plasma membrane Carbohydrates: help with cell to cell recognition Lipids (cholesterol): helps membrane remain flexible without becoming too loose or too rigid only in animal cells Proteins surface or transmembrane amount and type vary by cell type
Functions of plasma membrane proteins Support Intercellular junctions Cell-cell recognition Enzymes Signal transduction message transfer Transport
Movement of molecules across a plasma membrane Diffusion Osmosis Active transport Endocytosis & exocytosis
Diffusion The movement of particles down a concentration gradient no cellular energy! Types of Diffusion: Simple diffusion Facilitated diffusion uses transport protein
Osmosis The diffusion of water molecules across a selectively permeable membrane no cellular energy! What kind of energy is needed? How do cells control osmosis?
Water balance between a cell & its environment Tonicity: the relative solute gradient across a semipermeable barrier Why we care: This dictates water movement across the plasma membrane of living cells!
Water balance between a cell & its environment Tonicity: three possibilities! Hypertonic solution Hypotonic solution Isotonic solution
Active transport Moving against a concentration gradient Uses cellular energy! Uses transport protein
Moving large molecules across a plasma membrane Endocytosis importing materials How we eat and poop at the cellular level! Exocytosis exporting materials Both use cellular energy!!
Endocytosis Three different ways of getting things into a cell via endocytosis 1. Phagocytosis 2. Pinocytosis 3. Receptor-Mediated Endocytosis
Endocytosis, cont. White blood cell engulfing a yeast cell An amoeba showing pinocytosis
Exocytosis
Questions: What is the relationship among simple diffusion, facilitated diffusion and osmosis? How are these three concepts related to active transport? How are they different?
A few important organelles Nucleus, the largest organelle controls most cellular activities by directing the production of molecules stores genetic information nuclear membrane made of TWO phospholipid bilayers with pores to allow passages of materials
A few important organelles Mitochondria makes energy molecule ATP to fuel cellular work site of cellular respiration found in nearly every eukaryotic cell; #s vary by cell type two membranes (an inner & outer) contains circular DNA with instructions for making proteins necessary for energy conversion
A few important organelles Chloroplasts; in plants converts light energy into chemical energy site of photosynthesis two membranes similar in structure to mitochondria contains circular DNA with genes essential for photosynthesis
Talk to your neighbor Where did organelles come from? In other words, how did eukaryotic cells ever get organelles in the first place?
Endosymbiosis theory Mitochondria & chloroplasts were once small prokaryotes that began living in larger prokaryotes Over time, the endosymbiont & the host both benefited from the relationship Eventually, they grew increasingly dependent on each other until they could not live w/o each other became a single, more complex organism
Evidence of endosymbiosis theory: mitochondria & chloroplasts... Both are similar in size to prokaryotes Both are surrounded by a double membrane inner membrane has many similarities to prokaryotic membranes Both contain their own DNA DNA is circular like prokaryotic DNA Both contain their own ribosomes more similar to prokaryotic ribosomes than to eukaryotic ribosomes Both reproduce by a splitting process similar to some prokaryotes