Cell structure and function 2007-2008

Cell Theory: All living things are made of cells Cells are the basic unit of structure and function in an organism (basic unit of life) Cells come from the reproduction of existing cells.

Cell sizes and types Cells can only be observed under microscope Three Basic types of cells include: animal plant bacteria

Number of cells Although ALL living things are made of cells, organisms may be: Unicellular – composed of one cell Multicellular- composed of many cells

Prokaryote bacteria cells Eukaryote animal cells Types of cells Prokaryote bacteria cells Eukaryote animal cells Eukaryote plant cells

Prokaryotes Cells that lack a nucleus and membrane-bound organelles Ex: bacteria Simplest type of cell Single, circular piece of DNA

Eukaryotes Cells that HAVE a nucleus and membrane-bound organelles Ex: protists, fungi, plants, and animals More complex type of cells

ATP Cell Jobs make proteins make energy build more cells proteins control every cell function make energy for daily life for growth build more cells growth reproduction repair ATP

Limits to cell size Lower limit Upper limit most bacteria 1-10 microns Upper limit eukaryotic cells 10-100 microns diameter of human hair = ~20 microns

Why are cells small? Surface area to volume ratio V increases faster than SA Large cells cannot move material in & out fast enough to support life square - cube law As cell gets larger, volume increases cubically, but surface area only increases by the square. The volume of the cell is demanding… it needs exchange. The surface area is the exchange system… as cell gets larger, the surface area cannot keep up with demand. Instead of getting bigger, cell divides -- mitosis. s:v 6:1

How to get bigger? Become multicellular (cell divides) aa O2 aa aa aa NH3 O2 CH CHO aa O2 CH CHO CO2 Larger organisms do not generally have larger cells than smaller organisms — simply more cells What’s challenges do you have to solve now? how to bathe all cells in fluid that brings nutrients to each & removes wastes from each aa NH3 CHO CH O2 aa

The Cell: Nucleus, Ribosomes 2005-2006

Nucleus Function contains DNA some genes located in mitochondria & chloroplasts

Nucleus structure double membrane  nuclear envelope Pores (membrane fused) allow materials to pass through What kind of molecules need to pass through? RNA

Nucleus structure DNA organized into fibers called chromatin chromatin fibers coil up as separate chromosomes prior to division

Nucleolous produces ribosomes from rRNA & proteins

The Cell: Mitochondria & Chloroplasts

Overview Mitochondria & chloroplasts are organelles that convert energy to a form that cells can use for work mitochondria: from glucose to ATP chloroplasts: from sunlight to ATP & carbohydrates ATP = active energy carbohydrates = stored energy ATP + ATP

Mitochondria & Chloroplasts Similarities to each other (and bacteria) transform energy (generate ATP) double membranes = 2 semi-autonomous  move, change shape, divide have their own ribosomes, DNA & enzymes

Mitochondria Function cellular respiration generate ATP from breakdown of sugars, fats & other fuels in the presence of oxygen = aerobic respiration

Mitochondria Structure 2 membranes smooth outer membrane highly folded inner membrane cristae fluid-filled space between 2 membranes internal fluid-filled space mitochondrial matrix DNA, ribosomes & enzymes Why 2 membranes? increase surface area for membrane-bound enzymes that synthesize ATP

Dividing Mitochondria DIVIDE like bacteria REMEMBER ENDOSYMBIOSIS

Mitochondria Almost all eukaryotic cells have mitochondria number of mitochondria is correlated with aerobic metabolic activity more activity = more energy needed = more mitochondria What cells would have a lot of mitochondria? active cells: • muscle cells • nerve cells

increase surface area for membrane-bound enzymes that synthesize ATP Chloroplasts Structure 2 membranes outer membrane inner membrane internal fluid-filled space = stroma DNA, ribosomes & enzymes thylakoids = membranous sacs where ATP is made grana = stacks of thylakoids Why internal sac membranes? increase surface area for membrane-bound enzymes that synthesize ATP

Who else divides like that? Chloroplasts Function photosynthesis generate ATP & synthesize sugars transform solar energy into chemical energy produce sugars from CO2 & H2O Semi-autonomous moving, changing shape & dividing can reproduce by pinching in two Who else divides like that? bacteria!

Mitochondria & chloroplasts are different from other organelles not part of endomembrane system Grow & reproduce  semi-autonomous Proteins from ribosomes Contain circular chromosome directs synthesis of proteins produced by own internal ribosomes Who else has a circular chromosome bound within a nucleus? bacteria

Endosymbiosis theory Mitochondria & chloroplasts were once free living bacteria that were engulfed by ancestral eukaryote Endosymbiont cell that lives within another cell (host) partnership evolutionary advantage for both one supplies energy the other supplies raw materials & protection LICHENS = fungi & algae Lynn Margulis From hypothesis to theory! Paradigm shifting ideas in evolutionary biology.