LECTURE 3 CELL STRUCTURE

LECTURE 3 CELL STRUCTURE

HISTORY The cell was first discovered by Robert Hooke in 1665 examining very thin slices of cork and saw a multitude of tiny pores that remarked looked like the walled compartments of a honeycomb which was then called cells The description of these cells (which The description of these cells (which were actually non-living cell walls), without structure or function understanding, was published in Micrographia. His cell observations gave no indication of the nucleus and other organelles found in most living cells.

CELL THEORY Cell theory refers to the idea that cells are the basic unit of structure in every living thing. Cell Theory (the study of cells is cytology) All organisms are composed of one or more cells. The cell is the basic living unit of organization for all living things All cells arise from preexisting cells Cells contain all of the hereditary information Basic structures of all cell types: plasma membrane - a physical boundary that separates the cell from the outside environment organelles- internal structures that are suspended I the cytoplasm cytoplasm sort of jelly-like like substance, mostly water.

Types of cells Cells can be subdivided into the following subcategories: Prokaryotes: Prokaryotes lack a nucleus (though they do have circular DNA) and other membrane-bound organelles (though they do contain ribosomes). Bacteria and Archaea are two divisions of prokaryotes. Eukaryotes: Eukaryotes, on the other hand, have distinct nuclei and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles). In addition, they possess organized chromosomes which store genetic material.

Prokaryotes vseukaryotes Prokaryotes Includes cyanobacteriaand bacteria lack most of the membrane bound organelles, have DNA in a concentrated region, tend to grow rapidly and divide often. prokaryotes (0.2 5 µm) smaller than eukaryotes Eukaryotes Protists, fungi, plants and animals specialized membrane bound organelles (nucleus), nuclear membrane eukaryotes (10 100 µm)

Prokaryotic Cell Nucleoid: DNA concentration No organelles with membranes Ribosomes: protein synthesis Plasma membrane (all cells); semi-permeable Cytoplasm/cytosol (all cells) In a prokaryotic cell, most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic cell membrane.

Structure of Eukaryotic Cell All eukaryotic cells have a number of features in common. nucleus cytoplasm cell (plasma) membrane mitochondria endoplasmic reticulum Golgi apparatus ribosomes Cytoskeleton cenriole However, there are also some important differences between animal cells and plant cells.

Plant Cell

Comparison of animal and plant cells Both animal (A) and plant (B) cells have a cell membrane (1), nucleus (2), and cytoplasm (3). Plant cells have also a cell wall (4) and certain organelles, notably chloroplasts, which are unique to plant cells

Cell Size and Shape Cell Size Surface to volume ratio limits size of cell. Volume increases at the cube of the diameter (V=d 3 ) Surface area increases at the square of the diameter (A=d 2 ) As a cell grows its volume increases at a rate faster than its surface area Rates of chemical exchange may then be inadequate for cell size Cell size, therefore, remains small Cell Shape Form follows function similar functions in different organisms have similar shapes

Cell size

Cell Structure 1. Cytoplasm material outside of nucleus, consists of fluid and particles and membranes 2. Nucleoplasm material inside nucleus 3. Nucleus largest organelle Nuclear envelope Double Membrane envelope with many nuclear pores 4. Nucleolus (nuceioli plural) Site of ribosome assembly Ribosomes leave through pores and are found free in the cytoplasm or associated with Endoplasmic reticulum

Genetic material in the Nucleus Chromatin Seen in cells that are not dividing DecondensedDNA associated with RNA and proteins Chromosomes Seen in cells that are dividing Condensed DNA in a highly organized and compact form nucleolus: rrna; ribosome synthesis

5. Ribosomes Protein manufacture, organelles that are part of the protiensynthesis machinery Free : cytosol; protein function in cell Bound : endoplasmic reticulum; membranes, organelles, and export

6. Endoplasmic reticulum (ER) sets of membranes continuous with the nuclear and plasma membranes Membranes act to divide up the cytoplasm into compartments and channels Smooth ER no ribosomes; Functions: synthesis of lipids, phosolipid&steroid ; metabolism of carbohydrates; detoxification of drugs and poisons Rough ER with ribosomes; Functions: synthesis of secretory proteins (glycoproteins) & membrane production

7. Golgi Complex Cisternae: flattened membranous sacs (look like a stack of pita bread) sets of smooth membranes derived from the ER Functions: sorting and modifying proteins, ultimately transports products to the plasma membrane or are stored in the cytoplasm, also produces the lysosomes

8. Lysosomes(in animals) sac of hydrolytic enzymes (powerful digestive enzymes); digestion of macromolecules Function as the cell s recycling center by digesting worn-out organelles or materials ingested by cell: Phagocytosis Autophagy: recycle cell s own organic material Tay-Sachs disease~lipiddigestion disorder Rheumatoid arthritis is due to damage in joints due to leaky white blood cell lysosomes

9. Vacuoles membrane-bound sacs (larger than vesicles) Food (phagocytosis) Contractile (pump excess water) Central (storage in plants) tonoplast membrane

10.Mitochondria quantity in cell correlated with metabolic activity; cellular respiration; double membranous (phospholipid); cristae/matrix; intermembrane space; contain own DNA

11. Chloroplasts Type of plastid; Site of photosynthesis & Also double membrane bound thylakoids(flattened disks); grana(stacked thylakoids); stroma; Pigments (chorophyl and others) Also have their own DNA molecules

12.Other plastids leukoplasts store starch and are colorless, and chromoplasts store colored pigments

13. Microbodies Various organelles which regulate different metabolic reactions such as peroxisomes, single membrane break down hydrogen peroxide then converted to water, Metabolism of fatty acids; detoxification of alcohol (liver) glyoxysomesare important in germiniating seeds Organelles involved with Energy Production and Utilization

14. The Cytoskeleton Fibrous network in cytoplasm Support, cell motility, biochemical regulation Microtubules: thickest; tubulin protein; shape, support, transport, chromosome separation Microfilaments : Thinnest; actin protein filaments; motility, cell division, shape Intermediate filaments: middle diameter; keratin; shape, nucleus anchorage

15.Cell Wall

15. Membrane The membrane that surrounds a cell is made up of proteins and lipids. Depending on the membrane s location and role in the body, lipids can make up anywhere from 20 to 80 percent of the membrane, with the remainder being proteins. Cholesterol, which is not found in plant cells, is a type of lipid that helps stiffen the membrane.

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