Cell Structure. Cells. Why are cells so small? 9/15/2016. Schleiden and Schwann proposed Cell Theory in

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1 Cell Structure Cells Cells are sacs of fluid that are reinforced by proteins and surrounded by membranes. Inside the fluid float organelles. Organelles: structures inside the cell that are used for metabolic processes. The organs of the cell. Robert Hooke 1665 Why are cells so small? Surface area-to-volume ratio Efficiency Specialization Schleiden and Schwann proposed Cell Theory in

2 Need more surface area? Some cells overcome limitation by being long and skinny like neurons and some muscle cells. Basic properties of ALL cells Plasma membrane: encloses the cell and separates it from its surroundings. Nucleus (or nucleoid): Centrally located genetic material - DNA. Cytoplasm: semifluid matrix. Ribosomes: to synthesize proteins. Three Domains of Life Life on Earth can be grouped into three Domains. Domains: Bacteria-single-celled prokaryote Archaea-single-celled prokaryote Eukarya everything else (single-celled or multicellular eukaryote) Prokaryotic Cells (Bacteria & Archaea) Simplest organisms. Lack a membranebound nucleus. DNA is present in the nucleoid center loose, circular form. Cell wall outside of plasma membrane. Do contain ribosomes (but not membranebound organelles). 12 2

3 13 Flagella Present in some prokaryotic cells. May be one or more or none. Used for locomotion. Rotary motion propels the cell Two common pathogenic bacteria Streptococcus E. coli Benefits of Bacteria Probiotic cultures help with digestion. Used in food production e.g. yogurt, cheese. Help break down unwanted organics e.g. spilled oil, sewage. Can help with disease prevention helpful bacteria on skin can prevent colonization by pathogenic bacteria. Decompose organic matter releasing nutrients. Fix nitrogen from air, converting it into a form that plants can use. 18 3

4 Cyanobacteria The most complex prokaryote. Photosynthetic produce oxygen. Eukaryotic Cells Possess a membrane-bound nucleus. More complexthan prokaryotic cells. Hallmark is compartmentalization. Achieved through use of membrane-bound organelles and endomembrane system. Possess a cytoskeletonfor support and to maintain cellular structure. 24 4

5 Endomembrane System Series of membranes throughout the cytoplasm. Divides cell into compartments where different cellular functions occur Nucleus Repository of the genetic information. Nucleolus center region of nucleus where ribosomal RNA synthesis takes place. Nuclear envelope membrane of the nucleus. 2 phospholipid bilayers Nuclear pores Nuclear lamina Nucleolus Zone or region where intensive synthesis of ribosomal RNA is taking place. Genes for making ribosomal RNA are clustered together on the DNA strands, thus intensive transcription of these genes appears as a cluster: the nucleolus. 5

6 Nuclear Pores Diagram Micrograph Chromatin DNA that is spread out loosely, making it easier for it to be copied (RNA). Proteins attach in this form. DNA compacts into the X- shaped chromosome form for cell division (reproduction). Endoplasmic Reticulum The largest internal membrane. Interior space called the cisternal space or lumen. Rough endoplasmic reticulum (RER) Smooth endoplasmic reticulum (SER) Ratio of RER to SER depends on cell s function. 6

7 40 Smooth ER Relatively few bound ribosomes. Embedded enzymes in the membrane. These enzymes synthesize a variety of carbohydrates and lipids including steroid hormones & membrane lipids. 7

8 9/15/2016 Rough Smooth 44 Golgi Body (Apparatus) Functions to collect, package, and distribute molecules that have been synthesized at one location and need to go to another. Also modifies molecules and makes lysosomes. Has a front and back: a receiving end (cis face) and a distributing end (trans face). Trans face produces secretory vesicles for transport of molecules. 48 8

9 50 51 Lysosomes A type of membranebounded digestive vesicles that arise from the Golgi apparatus. Enzymes catalyzebreakdown of macromolecules digest food and release nutrients. Break down old organelles and recycle the component molecules. Destroy cells or foreign matter that has entered the cell. 54 9

10 Microbodies Variety of enzyme-bearing, membrane-enclosed vesicles. Peroxisomes Contain enzymes involved in the oxidation of fatty acids. Hydrogen Peroxide (H 2 O 2 ) produced as by-product of other enzymes rendered harmless by catalase in peroxisomes. Broken into water and oxygen Mitochondria Cellular generators. Carry out cellular respiration. Metabolize (convert) energy from food (like sugars) to generate ATP. Oxidative metabolism (requires oxygen to do this). ATP: adenosine triphosphate. ATP is cellular fuel; the main energy source for cellular functions. Mitochondria Structure Has an inner and outer membrane. Foldsof the inner membrane are called crista. Contain ribosomes. The inner membrane has embedded proteins. Ribosomes and enzymes are in the matrix(inside space). Mitochondria have their own DNA with genes to produce its needed proteins (like a cell within a cell). A simple, singular, circular DNA. Endosymbiosis Proposes that mitochondria and chloroplasts evolved from free living prokaryotes. One cell, a prokaryote, was engulfed by and became part of another cell, a precursor of modern eukaryotes

11 Microfilaments (actin filaments) Two protein chains loosely twined together. Support & Movements like contraction, crawling, pinching. Microtubules Largest of the cytoskeletal elements. Shape & support; trails for some organelles. Intermediate filaments Between the size of actin filaments and microtubules. Very structural, shape cell; anchor some organelles. Permanent fixtures. Nucleus has a cage of these. 62 Centrosome The centrosomeis an organelle that is the main place where cell microtubules get organized. Centriolesare located in, and form part of, the centrosome where they are paired structures lying at right angles to one another. Centrioles move towards the poles (opposite ends) of the nucleus when it is time for cell division. Extracellular matrix (ECM) Glycoproteinssecreted into the space around the cell. Includes collagen and elastin. Form a protective layer like a scaffoldover the cell. Integrins link ECM to cell s cytoskeletonthrough the plasma membrane. Influence cell behavior and coordinate cell behavior

12 Chloroplasts Organelles present in cells of plants (and a few others). Contain chlorophyll for photosynthesis. Converts light energy from the sun into sugar molecules (glucose). Have their own DNA (very similar to mitochondria) Chloroplast structure Inner and outer membranes. Disc shaped sacs: Thylakoids. Have light-capturing pigments on their surface. Granum: a stack of thylakoids. (Plural: grana). Stroma: thick, watery fluid inside the chloroplast that contains ribosomes, enzymes and DNA. 12

13 73 Plant Cell Wall Composed of fibers of the polysaccharide cellulose. Double wall: Primary and Secondary wall. Between walls of adjacent cells is middle lamella. This substance is sticky and helps glue the cells together. 13