Chp. 4 Cell Structure and Function

Prokaryote bacteria cells Eukaryote animal cells Types of cells Prokaryote bacteria cells - no organelles - organelles Eukaryote animal cells Eukaryote plant cells

Prokaryotic Cells No nucleus, no membrane-bound organelles But, they do have a cell membrane and they do have an organelle Ribosomes! Also have Nucleoid region, Cell Wall, and Cytosol (fluid)

Eukaryotic Cells Eukaryotic Cells contain a nucleus and membrane-bound organelles The membrane is key!

How big is a cell? Cells Alive! How Big is a Cell? Most cells are between 1 and 100 μm (10-6 or 1/ 1,000,000 m) Eukaryotic Cells are larger than prokaryotic cells

Limits to Cell Size As a cell grows, its surface area to volume ratio decreases This means the cell has more volume that needs to get oxygen, food, get rid of waste but less SA to do it over (in proportion)

Why organelles? Specialized structures Containers mitochondria Why organelles? Specialized structures specialized functions cilia or flagella for locomotion Containers partition cell into compartments create different local environments separate pH, or concentration of materials distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions unique combinations of lipids & proteins embedded enzymes & reaction centers chloroplasts & mitochondria chloroplast Golgi Why organelles? There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions. Organelles as specialized structures An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move. Organelles as Containers Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it. Organelle membranes as sites for chemical reactions An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast. ER 8

Cells gotta work to live! What jobs do cells have to do? Make proteins proteins control every cell function Store energy for daily life for growth Make more cells growth repair renewal 9

Proteins do all the work! DNA cells Repeat after me… Proteins do all the work! organism

Cell functions Building proteins 1. read DNA instructions 2. build proteins 3. process proteins folding modifying removing amino acids adding other molecules e.g, making glycoproteins for cell membrane 4. address & transport proteins

Building Proteins Organelles involved nucleus ribosomes endoplasmic reticulum (ER) Golgi apparatus vesicles The Protein Assembly Line Golgi apparatus nucleus ribosome ER vesicles

Nucleus Function Structure protects DNA nuclear envelope histone protein chromosome DNA Function protects DNA Structure nuclear envelope double membrane membrane fused in spots to create pores allows large macromolecules to pass through nuclear pores pore nuclear envelope nucleolus 13

production of mRNA from DNA in nucleus nuclear membrane 1 production of mRNA from DNA in nucleus small ribosomal subunit large cytoplasm mRNA nuclear pore 2 mRNA travels from nucleus to ribosome in cytoplasm through nuclear pore 14

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Nucleolus Function ribosome production build ribosome subunits from rRNA & proteins exit through nuclear pores to cytoplasm & combine to form functional ribosomes small subunit large subunit ribosome rRNA & proteins nucleolus 16

Ribosomes Function Structure protein production rRNA & protein small subunit large Function protein production Structure rRNA & protein 2 subunits combine 0.08mm Ribosomes Rough ER Smooth The genes for rRNA have the greatest commonality among all living things. There is very little difference in the DNA sequence of the rRNA genes in a humans vs. a bacteria. Means that this function (building of a ribosome) is so integral to life that every cell does it almost exactly the same way. Change a base and this changes the structure of the RNA which causes it to not function. 17

Types of Ribosomes Free ribosomes Bound ribosomes suspended in cytosol synthesize proteins that function in cytosol Bound ribosomes attached to endoplasmic reticulum synthesize proteins for export or for membranes membrane proteins 18

Endoplasmic Reticulum Function processes proteins manufactures membranes synthesis & hydrolysis of many compounds Structure membrane connected to nuclear envelope & extends throughout cell accounts for 50% membranes in eukaryotic cell 19

Types of ER rough smooth 20

Smooth ER function Membrane production Many metabolic processes synthesis synthesize lipids oils, phospholipids, steroids & sex hormones hydrolysis hydrolyze glycogen into glucose in liver detoxify drugs & poisons ex. alcohol & barbiturates 21

Membrane Factory Build new membrane synthesize phospholipids builds membranes ER membrane expands bud off & transfer to other parts of cell that need membranes 22

Rough ER function Produce proteins for export out of cell protein secreting cells packaged into transport vesicles for export Which cells have a lot of ER? protein production cells like pancreas = production of digestive enzymes (rough endoplasmic reticulum from a cell of exocrine pancreas (88000X)) 23

Synthesizing proteins cytoplasm cisternal space mRNA ribosome membrane of endoplasmic reticulum polypeptide signal sequence ribosome

Golgi Apparatus Function finishes, sorts, tags & ships cell products like “UPS shipping department” ships products in vesicles membrane sacs “UPS trucks” transport vesicles secretory vesicles Cells specialized for secretion? endocrine glands: produce hormones pituitary, pancreas, adrenal, testes, ovaries exocrine glands: produce digestive enzymes & other products pancreas, mammary glands, sweat glands 25

Golgi Apparatus

Vesicle transport vesicle budding from rough ER fusion of vesicle with Golgi apparatus migrating transport protein ribosome

endoplasmic reticulum protein on its way! nucleus DNA TO: RNA vesicle TO: TO: vesicle ribosomes TO: protein finished protein Golgi apparatus Making Proteins 28

Making proteins Putting it together… cytoplasm nucleus cell membrane transport vesicle Golgi apparatus smooth ER rough ER nuclear pore nucleus ribosome cell membrane protein secreted cytoplasm 29

Lysosomes •Sac of hydrolytic enzymes; intracellular digestion of macromolecules Phagocytosis Autophagy: recycle cell’s own organic material Apoptosis: programmed cell death

Vacuoles Membrane-bound sacs digestion & release of cellular waste Food (phagocytosis) Contractile (pump excess water) Central (storage in plants) Unique to plants

Mitochondria Quantity in cell correlated with metabolic activity cellular respiration double membrane (phospholipid); Outer membrane is smooth Inner membrane is highly convoluted forming folds called cristae Contains enzymes used for ATP production •contain own DNA

Chloroplast Contains chlorophyll, captures energy from Sun and converts it to chemical bond energy via photosynthesis Structure: double membrane, contains thylakoids (flattened disks), grana (stacked thylakoids), stroma. own DNA Unique to plants and other photosynthesizers.

The Cytoskeleton Fibrous network in cytoplasm Support, cell motility, anchors and moves around organelles. Made of Actin Intermediate filaments Microtubules