Unit 2 : Cell Structure and Function

  1. Discovery of cells

    1. Robert Hooke= examined thin slices of cork and observed tiny, hollow compartment called cells

    2. Anton Van Leeuwenhoek- first to describe a living cell, animacles

    3. Schleiden and Schwann-scientists who were the first to establish that both plant and animal were made of cells

  2. Cell theory postulates 

    1. cell is the basic unit of life

    2. all organisms are made of cells(Schleiden and Schwann)

    3. all cells come from a common ancestor

      1. Weissman in 1880 added to cell theory that every cell comes from a common ancestor.

      2. Virchow stated that cells divide to form more cells

  3. Prokaryotic and Eukaryotic cells

    1. Prokaryotic

      1. Most simple and primitive cells, DNA is not delimited by a nuclear membrane

      2. their main group are bacteria 

      3. lack membrane bound organelles and are smaller in size 

      4. cell membrane made up of phospholipids, a cell wall made up of peptidoglycan

      5. flagella for locomotion

    2. Eukaryotic cells

      1. Endosymbiotic theory- explains the origin of eukaryotic cells from prokaryotes. States that eukaryotic cells evolved from prokaryotic cells that fused together. Mitochondria and chloroplast have their DNA and double membrane

      2. characterized from having membranous organelles, highly organized  

      3. they have a true nucleus, where the DNA is covered by a membrane

      4. animal and plant cells

  4. Cell functions 

    1. Make energy= make energy for activities, need to to clean up waste produced while making energy

      1. metabolic rxns-photosynthesis, chloroplast, cellular respiration, mitochondria

    2. Make proteins

      1. proteins do all the work in a cell

      2. ribosomes 

    3. Make more cells

      1. for growth, to replace damaged or diseased cells

  5. why organelles?

    1. each have a specialized structure and specialized functions

    2. partition cell into compartments

    3. create different local environments

      1. separate Ph or concentration of materials

      2. distinct and incompatible functions

  6. CEll  ORGANELLES

    1. Cell wall

      1. in plant cells, outermost shell of the cell, composed of cellulose and H2O 

      2. helps maintain the cell structure

      3. cell walls protect the cell, maintain its shape, prevent excessive water uptake and support the plant against gravity

        1. Primary cell wall- starts as thin and flexible, develops from the cell plate after cell division; once the plant matures, it hardens to be more supportive 

        2. secondary cell wall-found under the primary cell wall to strengthen it, it's not in every plants, it's very strong 

        3. middle lamella-glues plant cells together

    2. Cell membrane

      1. cover that protects and isolates the cell

      2. regulates the internal and external movement of materials in the cell

      3. helps the cell maintain the form and achieve cell-to-cell communication

      4. also found in prokaryotic cells

      5. small molecules and nonpolar can pass through the lipid bilayer without the necessity of a protein

      6. Functions

        1. separates cell from outside

        2. controls what enters and leaves cell

          1. O2, CO2, H2O, nutrients and waste

        3. recognizes signals from other cells, allows communication between cells

      7. Structure

        1. Phospholipid bilayer , receptor molecule( protein, cholesterol, carbohydrates)

      8. Animal cells

        1. extracellular matrix- provides support, adhesion, movement and regulation, structure that is found outside the animal cells. Bc they dont have a cell wall they need this to support. Composed mainly of glycoproteins, collagen

          1. help w flexibility movement and support

    3. Cytoplasm

      1. jelly-like material holding organelles in place, it has a liquid part, the cytosol

    4. Nucleus

      1. found in the center of the cell, biggest organelle and has a double membrane- DNA TO RNA

      2. controls all the activities in the cell and has phonetic information necessary for its proper functioning

      3. Nuclear pore- exchange of materials with the nucleus RNA leaves through here

      4. nucleoplasm-the cytoplasm in the nucleus

      5. chromatin- DNA condensed 

      6. nucleolus- synthesis of ribosomes, dense region where builds ribosome subunits from rRNA and proteins

        1. exit through nuclear pore to cytoplasm and combine to form functional ribosomes


  1. Endomembrane system

    1. A system in internal membrane which includes  

      1. Nuclear envelope, ER, golgi apparatus and plasma membrane, lysosomes, vesicles and vacuoles

  2. Endoplasmic reticulum

    1. interconnected network of thin folded membranes

    2. helps with synthesis of lipids and proteins starting point of the transport vesicles that move proteins inside the cell

      1. Smooth ER: produces lípids, Also used in breaking down drugs and alcohols

        1. Function: membrane production; many metabolic processes. Synthesis= lipids oils and phospholipids and steroids. They hydrolize glycogen into glucose

        2. detoxify

      2. Rough ER: surface covered with ribosomes. Protein synthesis

        1. Function: finalize formation and prepare for export out of the cell(protein folding)

        2. proteins secreting cells with have lots 

        3. packaged into transport vesicles to golgi

  3. Ribosomes

    1. tiny organelles that link amino acids to form proteins 

    2. Made of ribosomal RNA and proteins

    3. location- cytosol: free ribosomes/ RE: bind ribosomes

    4. made up of subunits- major subunit and minor subunits

  4. golgi apparatus

    1. consists of sacs

    2. Functions= 

      1. 1. modifies products of ER

      2. produces molecules

      3. sorts and packs materials in transport vesicles mainly proteins

      4. 2 faced

        1. trans face- exit of molecules

        2. cis face- lado de recepcion, receives molecules

  5. Lysosomes

    1. Only found in animal cells, help break down organic waste material. digestive compartments of the cells sacs of enzymes; can digest or destroy dangerous materials that are taken into the cell(phagocytosis)Some are formed from budding from the golgi, these play an important role in embryo development and also in programmed cell death

    2. apoptosis- auto-destruct process, lysosomes break open and kill cell.

  6. peroxisomes

    1. sacs that contain various enzymes in wich occur a lot of metabolic rxns.

    2. Produce hydrogen peroxide as a byproduct but then immediately break it down into water and oxygen 

  7. glycosomes-sacs that store carbohydrates

  8. Vacuole- membranous sacs, mainly in plants, algae and fungi, that help with the transport and storage of materials, waste and water

    1. Function in plant cells

      1. 1. storage- stockpiling proteins or inorganic ions.

        1. depositing metabolic byproducts 

        2. storing defensive compounds against herbivores

  9. Vacuoles

    1. Functions=

      1. little transfer ships

      2. in animal cells food vacuoles= phagocytosis fuse with lysosomes

      3. contractile vacuole- in freshwater protists, pumps excess H2O

      4. Central vacuoles- in many mature plant cells

  1. Energy organelles

    1. Mitochondria(semi autonomous)

      1. cellular respiration, generate ATP from breakdown of sugars, fats and other fuels, in the presence of oxygen

      2. Catabolism-breakdown larger molecules into smaller to generate energy

      3. aerobic respiration-generate energy in the presence of CO2

    2. Chloroplast(semi-autonomous)

      1. Function: photosynthesis, generate ATP and synthesize sugar 

      2. have their own DNA 

      3. contain green pigmentation(chlorophyll) enzymes and other molecules that help in the energy conversion process

      4. Structure- thylakoid, stroma

      5. belongs to a family of plant structures called plastids

      6. amyloplasts- colorless plastids that store starch in roots

      7. chromoplasts- store pigments for fruits and flowers, plastids that lack chlorophyll

      8. internal ribosomes, DNA and enzymes(also in mitochondria)

    3. Cytoskeleton

      1. Main purpose is to give form and reinforce the cell

      2. It gives shape to the cell, anchors the other organelles

      3. it can be easily dismantled in one part of the cell then reassembled in a new location, changing the shape of the cell

      4. Main cytoskeleton structure

        1. microtubules

        2. microfilaments or actinfilaments 

        3. centrosomes and centriole

          1. centrosomes help coordinate cell division, located near the nucleus  and this is where the microtubules are made

          2. centrioles are organelles that are found within centrosomes in animal cell and help with cell division

        4. intermediate filaments- made of fibrous proteins supercoiled into thicker cables. Function: maintenance of cell shape, anchoring nucleus and certain organelles

        5. microtubules-hollow tubes made of tubulin , they maintain cell shape, motility, chromosome movement in cell division, organelle movement

        6. cillia and flagella-main function movement, made of microtubules


CELL SIZE

  1. The logistics of carrying out cellular metabolism set limits on the cell size 

    1. cell size limits its efficiency and activities 

    2. cells that are too big will work harder to move things in and out of the cell 

    3. eukaryotic cells are organisms do not generally have larger cells than smaller organism, simply more cells.

    4. Cell diversity

      1. Cells are very diverse in terms of shape and internal organization

      2. their can can be complex or simple

    5. why are cells so small

      1. limits to cell size are to the logistics of carrying out cell functions

      2. having organelles to move materials around allows eukaryotic cells to be larger than prokaryotic cells


  1. Surface area 

    1. determines th exchange of matter between the cell and its env

    2. SA: V ratio

    3. it limits the size of the cell, as the surface area increases by a factor of n2 the volume increases by a factor of n3

    4. small cells have a greater surface area relative to volume 

    5. bigger cells will need more surface to support that metabolism

    6. as cells get bigger its volume increases faster than its surface area

    7. cell membrane limits the size 

    8. In a large cell, cannot move material in and out of cell fast enough to support life

  2. how to get bigger?

    1. become multicellular org

  3. multicellular organisms challenges

    1. it needs to make sure all cells get nutrients and fluids

    2. be able to remove waste



  1. volume

    1. determine the amount of metabolism in the cytoplasm. metabolism will require  import of precursors and result in export of secretions.

  2. Examples of surface area in animal cells

    1. small intestine- highly folded surface to increase absorption of nutrients

    2. villi: finger-like projections in SI wall

    3. microvilli: projections on each cell

    4. root hairs-extensions of root epidermal cells, increase surface area for absorbing water and minerals