Cell Theory

• Cells are fundamental units of life

• All organisms are composed of cells

• All cells come from preexisting cells

• same as studying life

• Life is continuous- we can trace back to cells

Cells like to keep a good surface area to volume ratio

• Volume determines metabolic activity per unit of time

• Surface area determines how many substances enter and leave

• Basically need a high ratio so that enough nutrients can enter and waste can exit for the processes to happen

• Cells increase surface area by folding

Cell Membrane

• made of lipids

• Selectively permeable barrier that helps maintain homeostasis

• Important in communication and receiving signals

• Has proteins for binding cells

  • Plasmodesmata are membrane-lined channels found in plants that transport substances and connect them

  • Extracellular matrices are found in animals

    • Like a string of webs connected to the membrane that hangs outside

      • Integrin connects the extracellular matrix to the membrane

      • Connected to microfilaments in the cell membrane and the collagen outside

      • for cell movement, the protein changes shape and detach

    • Fibrous component is collagen, gel-like component is proteoglycans

      • collagen is a protein, proteoglycans are proteins and polysaccharides

      • contribute to physical properties of bone, cartilage, skin, bone, and other tissues

      • help filter materials like in kidneys

      • orient cell movement and repair

  • Cell junctions protrude through and between cells to bind them together

    • Tight junction

      • prevents substances moving in the space between the cells

    • Desmosomes

      • allows for substances to move in the matrix between cells

    • Gap junction

      • run between membrane pores, allows for substances to pass through them

• Cell Wall

  • Bacteria

    • have cell wall containing peptidoglycan (amino sugars and saccharides)

    • some bacteria have a additional outer cell wall, very permeable

    • some have slimy layer of polysaccharides called the capsule

    • some bacteria, including cyanobacteria, contain molecules in membrane that can photosynthesize

  • plants

    • semi-rigid, provides support and limits its volume

    • cellulose

    • gel-like matrix contains proteins and polysaccharides

    • act as barrier to infection

    • contributes to form during growth

Organelles

• found in the cytoplasm along cytosol, which is water and dissolved particles

• Ribosomes

  • sites of protein synthesis

  • translates the nucleotide sequence of a messenger RNA into a polypeptide

  • both types of cells, has a large and a small subunit

  • 

  • each subunit consists of ribosomal RNA and protein

  • not membrane bound organelles

  • they are free in the cytoplasm, in the rough endoplasmic reticulum, or in mitochondria or chlorplast

  • in prokaryotes they float freely in the cytoplasm

• Nucleus

  • usually largest organelle

  • where DNA is stored and replicated

  • where DNA is transcribed to RNA

  • contains nucleolus

    • where ribosomes are made from RNA and proteins

  • two membranes called the nuclear envelope

    • has pores for substances to pass through

  • In the nucleus, DNA combines with proteins called chromatin to make chromosomes

    • strand of DNA encoded with genes

  • outer membrane is continuous with the endoplasmic reticulum

• endomembrane system

  • nuclear envelope, endoplasmic reticulum, golgi apparatus, and lysosomes

• vesicles

  • membrane-bound shuttles that transport substances between components and the membrane

• Endoplasmic reticulum

  • network of interconnected membranes in the cytoplasm, large surface area

  • Rough endoplasmic reticulum

    • ribosomes attached to surface

    • newly made proteins enter the RER lumen, and are modified then tagged for delivery to specific locations

      • transported in vesicles that pinch off of the ER

    • all secreted proteins and most membrane proteins pass through RER

    • Polypeptides also transported to RER while synthesizing

      • folded into tertiary structure

      • many combine with carbohydrate groups, becoming glycoproteins

        • important in recognition and interaction between cells

  • Smooth Endoplasmic Reticulum

    • more tubular (like coral, RER is wall-y), no ribosomes

    • chemically modifies small molecules like drugs and pesticides

    • site of glycogen degradation

    • synthesis of lipids and steroids

    • stores calcium ions, important for cell responses

• Golgi Apparatus

  • flattened sacs (cisternae) and small membrane enclosed vesicles

  • further modifies proteins from the RER

  • concentrates, packages, and sorts proteins

  • adds carbs to proteins

  • site of polysaccharide synthesis for plant cell walls

  • three regions

    • cis: recieves

    • trans: exports in vesicles to the membrane or lysosomes

    • medial: medial

• Lysosomes

  • primary lysosomes originate from golgi apparatus

  • contain hydrolases (digestive enzymes), macromolecules are hydrolyzed into monomers

  • macromolecules enter the cell through phagocytosis

    • part of the membrane encloses the material and a phagosome is formed

    • phagosomes then fuse with primary lysosomes to make secondary lysosomes

    • secondary lysosomes hydrolyze food molecules

  • phagocytes are cells that specialize in taking in materials and breaking them down

  • autophagy is the programmed destruction of cell components (materials and organelles) using lysosomes

  • lysomal storage diseases happen when lysosomes fail to break cell components down

• Mitochondria

  • energy-rich molecules begin breaking down in the cytosol

  • then it enters the mitochondria where it gets turned into ATP

  • need more energy=more mitochondria

  • 2 membranes

    • outer-very porous

    • extensive folds called cristae increase surface area

  • fluid filled matrix contains enzymes, DNA, and ribosomes

• peroxisomes

  • collect and break down toxic by-products of metabolism (ex. H2O2) using special enzymes

• plant organelles

  • plastids

    • some are used for storage

    • give plants their color

    • chromoplasts

    • leucoplasts (starch)

  • chloroplast

    • chlorophyll, photosynthesis, anabolic reaction

    • two membranes

    • internal membranes called thylakoids

      • granum- stack of thylakoids, converts light energy into chemical energy

      • stroma- aqueous matrix around grana

        • contains ribosomes and DNA, synthesizes carbs

  • glyoxysomes

    • convert lipids into carbs for growth

• vacuoles

  • mainly in plants and fungi

  • storage of waste in toxins, deters herbavores

  • structure for plants, water enters vacuole through osmosis, creates turgor pressure

  • reproduction- colors attract pollinators

  • catabolism- enzyme in seed vacuoles hydrolyze stored food for early growth

  • contractile vacuoles can get rid of water by pumping it out and moving the cell

Cytoskeleton

• some rod-shaped bacteria have network of actin-like, helical structures that help maintain shape

• supports and maintains cell shape

• holds organelles in position and can move them

• involved in cytoplasmic streaming (things in cell move)

• interacts with extracellular stuff to hold cell in place

• dynamic instability

  • filaments can lengthen or shorten with more assembly or detachment

    • actin and myosin interact to contract muscles

• motor protein

  • any protein that causes movement

• 3 components

• microfilaments

  • helps a cell or its parts move

  • determines shape

  • made from actin monomers that attach in the plus end and detach at the minus

    • actin is a protein, important in muscle contraction

• intermediate filaments

  • 50 kinds, 6 classes

  • tough, ropelike, no dynamic instability

  • anchor cells in place

• microtubules

  • thickest cytoskeleton component

  • rigid internal skeleton for some cells or regions

  • framework for motor proteins

  • made from dimers of protein tubulin, chains of dimers surround a hollow core

  • • and - ends, dynamic instability

  • polymerization - rigidity, depolymerization- collapse

  • form internal skeleton for cellular appendages

  • cilia

    • short, usually many

    • stiffly moves cell

    • can move fluid over a stationary cell

  • flagella

    • some prokaryotes use flagella to move

    • one or two, longer, push or pull cell through water

  • cilia and flagella microtubules are arranged in 9+2 pattern

    • doublets- 9 fused pairs of tubules form a cylinder

    • one unfused pair in center

    • motion occurs when doublets slide past each other

    • dynein

      • motor protein that can change shape, causes sliding

    • nexin

      • crosslinks doublets and prevents sliding, so it bends

    • kinesin

      • combines with vesicles that walk along the microtubule