BISC 101 - A Tour of the Cell - Student Copy PDF

Dr. Onkar S. Bains BISC 101 Overview: Cells are the fundamental units of life Within the levels of biological organization, cells are the simplest collection of matter that is alive As stated in the cell theory… – all organisms consist of cells – all cells are deriv...

Dr. Onkar S. Bains BISC 101 Overview: Cells are the fundamental units of life Within the levels of biological organization, cells are the simplest collection of matter that is alive As stated in the cell theory… – all organisms consist of cells – all cells are derived from pre- existing cells  Concept A: Two types of cells are prokaryotic and eukaryotic The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Bacteria and archaea consist of prokaryotic cells Protists, fungi, animals and plants consist of eukaryotic cells  Comparing prokaryotic and eukaryotic cells Basic features of all cells: – Plasma (or cell) membrane: o Separates interior environment of cell from outside environment of cell o Selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell Single human heart muscle cell beating o General structure of a biological membrane is a double layer (or bilayer) of phospholipids – DNA, the genetic material, is packaged into one or more chromosomes – Contain ribosomes (small complexes where protein synthesis takes place) – Has a semifluid substance within plasma membrane called cytosol (or cytoplasm)  Distinguishing characteristics of prokaryotic cells: – ONLY some have membrane-bound organelles (“compartments”) that perform specialized tasks like storing calcium ions and organizing enzymes for building organic compounds (they do not have the typical membrane-bound organelles found in eukaryotic cells) – Since there is no nucleus…DNA is found in a non-membrane bound region called the nucleoid region – Most prokaryotes have DNA packaged as a single, circular chromosome – Cytoplasm bound by the plasma membrane – Use binary fission, which is a type of asexual reproduction and cell division in which DNA is copied and cell splits into two genetically identical cells  Distinguishing characteristics of eukaryotic cells: – Membrane-bound organelles present (i.e., mitochondria, chloroplast, Golgi, nucleus, endoplasmic reticulum, etc.) – DNA in a nucleus that is bounded by a membranous nuclear envelope – DNA is packaged as multiple, linear chromosomes – Cytoplasm in region between plasma membrane and nucleus – Use mitosis, which is a type of asexual reproduction and cell division Eukaryotic cells are generally much larger than prokaryotic cells Concept B: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the DNA in a eukaryotic cell (a.k.a. “information central”) – Nuclear envelope encloses nucleus, separating it from the cytoplasm – This envelope is a double membrane; each membrane consists of a lipid bilayer – Pores regulate entry and exit of molecules from nucleus – DNA and proteins form genetic material called chromatin – Nucleolus is located within nucleus and is site of ribosomal RNA (rRNA) synthesis along with the large and small ribosomal subunits  Nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM) Attached to the inner nuclear membrane on the nucleoplasm side is the nuclear lamina. This is a sheet of proteins that provides support for and strengthens the nuclear envelope. The nuclear lamina also attaches to and anchors chromatin. Ribosomes: protein factories Ribosomes are particles made of ribosomal RNA and protein Uses the information from the DNA to make proteins during translation Carry out protein synthesis in two locations: – In the cytosol (free ribosomes) – On outside of endoplasmic reticulum or nuclear envelope (bound ribosomes) Concept C: The endomembrane system is composed of different membranes suspended in cytoplasm with eukaryotic cell Components of endomembrane system (i.e., “inner membrane” system) that we will cover are: – Nuclear envelope already looked in previous slides – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Plasma membrane The components work together to modify, package and transport lipids and proteins Endoplasmic reticulum: biosynthetic factory The endoplasmic reticulum (ER) accounts for about 50% of the total membrane in many eukaryotic cells ER membrane is continuous with (or connected to) nuclear envelope There are two distinct regions of ER: – Smooth ER, which lacks ribosomes – Rough ER, which has ribosomes on its surface Functions of smooth and rough ER Mainly involved in synthesis Has bound ribosomes, which are of lipids (i.e., phospholipids involved in production of proteins and steroids) (so mainly involved in protein synthesis) Detoxification (enzymes are embedded in smooth ER to convert toxic organic, lipid- soluble chemicals to safer water-soluble products so that they can be easily excreted from body) Stores calcium ions in muscle cells (these ions are found in sarcoplasmic reticulum, a type of smooth ER) Golgi apparatus: shipping and receiving center Consists of flattened membranous sacs (cisternae) Functions of the Golgi apparatus: – Modifies, sorts and packages different macromolecules for cell secretion (exocytosis) or use within the cell – Sorts and packages materials into transport vesicles  Lysosomes: digestive compartments A lysosome is a membrane- bound organelle that contains hydrolytic enzymes involved in digesting proteins, fats, nucleic acids, and carbohydrates – Note – lysosomes can also use Hydrolytic enzymes are active these enzymes to break down the cell’s own organelles in order to at acidic pH (about 5) that is be recycled (called autophagy) maintained within lysosomes but not at neutral pH (about 7), which is seen with rest of The acidic internal pH of lysosomes results the cytoplasm from the action of a proton pump in the – If lysosomal membrane were lysosomal membrane, to break down, the released which imports protons hydrolytic enzymes would be from the cytosol coupled to ATP inactive (denatured) at the hydrolysis neutral pH of cytoplasm Concept D: Mitochondria and chloroplasts change energy from one form to another Mitochondria are sites of cellular respiration, a metabolic process that generates ATP Chloroplasts, found in plants and algae, are the sites of photosynthesis Mitochondria and chloroplasts… – are not part of endomembrane system – have a double membrane – have proteins made by free ribosomes – contain their own DNA  Mitochondria: chemical energy conversion They have a smooth outer membrane and an inner membrane folded into cristae Major site of cellular respiration to generate ATP Internal fluid is called matrix Number of mitochondria in a cell can vary widely – For example, human red blood cells have no mitochondria while liver cells can have more than 2000!! Chloroplasts: capture of light energy Major site of photosynthesis Chloroplast structure includes: – Thylakoids (membranous sacs) stacked to form a granum – Stroma (internal fluid) Chloroplasts are found in leaves and other green organs granum of plants, as well as in algae – Chloroplasts are green because they contain the pigment chlorophyll in their thylakoids Concept E: Peroxisomes are important in breakdown of fatty acid molecules and alcohol as well as protection of cells from reactive oxygen species Not part of endomembrane system Has plasma membrane Contains crystalline core, which contains enzymes – Some enzymes involved in chemical breakdown (metabolism) of long chain fatty acids and alcohol Image on right: peroxisomes in dotted circles  Some of these enzymes help protect the cell from harmful reactive oxygen species (ROS) molecules – ROSs are molecules created as a product of normal cellular metabolism, but also by radiation, tobacco, and drugs (if left uncheck, ROSs can seriously damage cells) – They cause what is known as oxidative stress in the cell by reacting with and damaging DNA and lipid-based molecules like cell membranes Enzymes in peroxisomes that protect cells from ROSs are catalases, superoxide dismutases and peroxidases Concept F: The cytoskeleton is a network of fibers that organizes structures and activities in the cell The cytoskeleton is a network of fibers made up of protein subunits extending throughout the cytoplasm They make up the cellular scaffolding or skeleton contained within a cell's cytoplasm Cytoskeleton is composed of three types of molecular structures: – Microtubules – Microfilaments (or actin filaments) – Intermediate filaments Components of the cytoskeleton Three main types of fibers make up the cytoskeleton: – Microtubules are the thickest of the three components of the cytoskeleton – Microfilaments, also called actin filaments, are the thinnest components – Intermediate filaments are fibers with diameters in a middle range (two intertwined strands) (i.e., protein fibers are wound into thicker cables) MICROFILAMENT INTERMEDIATE FILAMENT MICROTUBULE  Some key roles of the cytoskeleton Maintenance of cell shape – involves microtubules, microfilaments and intermediate filaments Movement of organelles in a cell – involves microtubules – Organelles can travel along “monorails” provided by microtubules (interacts with motor proteins to generate movement) Anchorage of nucleus and certain other organelles in a cell – intermediate filaments (also involved in formation of nuclear lamina) Cytoplasmic streaming – involves microfilaments – Cytoplasmic streaming is a circular flow of cytoplasm within cells to allow for rapid distribution of materials within the cell  Cell motility – involves microtubules and microfilaments – Microtubules control the beating of cilia and flagella, which are locomotor appendages of some cells – Pseudopodia (literally means “false foot”) are temporary cytoplasmic extensions that are powered by microfilaments near the plasma membrane  Cell division – involves microtubules (for mitosis and meiosis) and microfilaments (for cytokinesis of animal cells) In cytokinesis, the cytoplasm of a parental cell is equally distributed into two daughter cells Concept G: Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include: – Cell walls of plants – Extracellular matrix (ECM) of animal cells – Intercellular junctions  Cell walls of plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Prokaryotes, fungi, and some protists also have cell walls The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein  The extracellular matrix (ECM) of animal cells Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin – Glycoproteins = proteins with covalently bonded carbohydrates – Collagen is the most abundant glycoprotein in the ECM of most animal cells (in fact, collagen accounts for ~40% of the total protein in the human body!) ECM proteins bind to receptor proteins in the plasma membrane called integrins Some key functions of the ECM include : – Structural support to cell, cell movement, and cell-to-cell signaling Core protein Intercellular junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact There are four types of intercellular junctions that we will briefly cover in this course: – Plasmodesmata – Tight junctions – Desmosomes – Gap junctions  Plasmodesmata are channels that perforate plant cell walls Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell  Tight junction At tight junctions, Tight junctions prevent fluid from moving across a layer of cells membranes of 0.5 µm neighboring cells are pressed together, preventing leakage of Tight junction extracellular fluid Intermediate filaments – So they form a water-tight Desmosome connection between adjacent cells (this means Gap Desmosome junctions 1 µm that in order for molecules to actually get past the cell, they have to first make their way into that cell!) Extracellular Space matrix between Gap junction cells Plasma membranes of adjacent cells 0.1 µm  Desmosomes (anchoring junctions) fasten cells Tight junctions prevent Tight junction together into strong fluid from moving across a layer of cells sheets – They attach to intermediate 0.5 µm filaments and hold two adjacent cells tightly together at a localized region Tight junction – So in a way the can act like Intermediate tight junctions BUT filaments desmosomes do not prevent Desmosome movement of molecules Desmosome around cells Gap 1 µm junctions Gap junctions (communicating junctions) provide cytoplasmic “channels” Extracellular Space matrix between Gap junction cells Plasma membranes or “tunnels” between of adjacent cells 0.1 µm adjacent cells Concept H: Differences between plant and animal cells 1. Plant cells have cell walls while animal cells do not (animal cells have an extracellular matrix) 2. Plant cells have chloroplasts while animals cells do not 3. Plant cells have a large central vacuole while animal cells have small vacuoles 4. Plant cells use starch as energy source while animal cells use glycogen 5. Most plant cells do not have lysosomes while animal cells have lysosomes 6. Plant cells are primarily autotrophic while animal cells are heterotrophic – Autotrophs are capable of producing their own food – Heterotrophs cannot make their own food, so they must eat or absorb it. 7. During cytokinesis, plant cells form a cell plate while animal cells form a cleavage furrow 8. Plant cells have plasmodesmata while animals cells have gap junctions