Chapter 6: Organisms in The Cell

The Cell Theory

1) All living organisms are made up of cells

2) All cells come from pre-existing cells

3) cells are the basic unit of life

  • The naked eye can see up to 0.2mm. Cells cannot be seen through the naked eye

  • Cells can be seen through microscopes

    • Light Microscopes- can distinguish objects up to 0.5 micrometers apart

    • Fluorescent Microscopes- can distinguish objects up to 20 nm

    • Electron Microscopes- can distinguish objects up to 1 nm

Why are cells small?

  • surface area/ volume ratio determines their size

  • Larger objects; smaller surface area/ volume ratio

  • Smaller objects; larger surface area/ volume ratio

    • Cells need large surface area & volume to transfer things in and out.

Prokaryotes VS. Eukaryotes

Common in Both:

  • Plasma Membrane- made of a lipid bilayer containing a hydrophilic head & hydrophobic tail.

    • Lipid bilayer is 2 layers of these heads and tails

    • Lipid bilayer also contains proteins

  • Genetic Material: DNA & RNA

    • DNA is needed in both prokaryotes & eukaryotes

  • Cytoplasm-

    • Eukaryotes: anything in between nuclear membrane and plasma membrane

    • Prokaryotes: anything inside the plasma membrane

  • Cytosol- Liquid (aq solution) where substance are disolved, fluid portion of cytoplasm

  • Ribosomes- complex of RNA/ Proteins

    • Cause for polypeptide synthesis (putting proteins together)

Prokaryotes

  • most abundant/ most diverse

  • Cell walls (outside plasma membrane). They provide support and structure

  • In some: flagella & fimbrae are present

  • DNA is circular bacterial genome

  • 3 Basic Shapes Associated with Prokaryotes

    • Spherical

    • Rod-shaped

    • Spiral

  • Not all bacteria is unicellular. Multicellular orangisms are in Prokaryotes & Eukaryotes.

Eukaryotes

  • have organelles-subcellular structures that are membrane-bound & have specific functions/structures

  • Nucleus-

    • contains most of DNA (nuclear DNA); part of chromatin

    • Chromatin is divided into units which makes up chromosomes

    • Within the nucleus there is a nucleolus; more dense region becasue there is more DNA. Therefore, synthesis of ribosomes .

  • Nuclear Membrane/ Nuclear Envelope-

    • double-membrane; 2 separate lipid bilayers

    • transport ions, protein, RNA in/out of nucleus through nuclear pores

    • Right underneath inner membrane is the matrix of proteins (Nuclear Lamina); its a mixture of proteins & provides structure, supports, gives shape to nucleus

  • Nucleolus-

    • denser region in nucleus. tends to hold more DNA.

  • Endomembrane System-

    • consists a number of organelles. Also continuous with outer membrane part of nucleus.

    • Endomembrane System consists of four organelles -

      • - Endoplasmic Recticulum

      • - Golgi Apparatus

      • - Lysosomes

      • - Peroxisome

    • All organelles in this system are continuous with each other.

  • Endoplasmic Recticulum (ER)

    • Smooth Er: there is nothing located on membrane

      • - sythesis of lipids

      • - Metabolizes some carbohydrates

      • - detoxifies toxins/drugs

      • - Stores calcium

    • Rough Er: Ribosomes are located on membrane surface

      • - Ribosomes sythesis(catalyze) of proteins part of endomembrane system.

      • - This leads to protein processing; Modification of Proteins.

      • - Functional groups and Carbohydrates are involved

  • Golgi Apparatus-

    • There is directionality; normally towards the plasma membrane

    • golgi recieves proteins from other molecules and further modifies them

      • - meaning it sorts + packages proteins & molecules to other parts of endomembrane system.

    • Synthesis of macromolecules

  • Lysosomes-

    • Sac of hydrolytic enzymes

    • this is where molecules are broken down through Hydrolysis (digestion)

    • Molecules to be broken down are ingested molecules. (Ex: food)

    • Old & broken down molecules inside cell are recycled

  • Peroxisome-

    • Contain hydrogen peroxide, which breaks down lipids

  • Mitochonria(plural) Mitochondrion(singular)

    • Double-Membrane

      • -inner membrane & outer membrane

      • inner membrane is highly folded & cristae

    • Cellular respiration, energy transfer occurs here

Other Eukaryotic Structures Below

  • Cell Wall-

    • Contains Celllous (most abundant molecule)

    • Cell Wall provides structure to support plant cell

  • Chloroplast-

    • Photosythesis: converts light energy into chemical energy, creating food for plants

    • Chloroplast contains and inner & outer membrane

    • Inner membrane is continuous with thylakoid membrane

  • Mitochondria & Chloroplast Evolution-

    • Endosymbiotic Theory: theorized that mitochondria came first

      • Engulfment of bacteria alive in cell led to a symbiotic relationship

      • Engulfed bacteria over time morphed into Mitochondria

    • For Chloroplast: earlier eukaryote with mitochondria engulfed photosynthesis, forming symbiotic relationship

    • Therefore, chloroplast was made

Plant Cells

  • Chloroplast-

    • Outer membrane

    • Inner membrane; in thylacoid membrane & involved in photosythesis

  • Central Vacuole-

    • Stores molecules and water

    • Type of vacuole; large vesical, which are from ER and Golgi

    • IN ANIMALS—> they contain a food vacuole instead

  • Cytoskeleton-

    • Includes support and structure, spatial organization and movement; intracellular transport

    • Divided into 3 parts: Types of cytoskeletons are fibers extending throughout cell.

      • - Microtubules (thick filaments)

      • - Microfilaments (thin filaments)

      • - Intermediate Filaments

1) Microtubules

  • hollow tubes polymer, made of proteins = alpha & beta tubulin dimers

  • Microtubules are organizing complex. However, mammals don’t need, ONLY PLANTS.

    • Instead animals have Centrosomes: big protein complex that includes pairs of centrioles

  • Microtubules contain 2 motor proteins, Dynein & Kinesin

    • these proteins “walk” on microtubule “tracks” to transport cargo

    • this is Intracellular Transport. This forms specialized structures:

      • - spindles forms through mitosis & meiosis

      • - binds chromosomes and seperates chromosomes

  • Flagella + Cilia-

    • For motility & movements

    • these structures are made up of microtubules

2) Intermediate Filaments

  • these are found in animal cells

  • do not contain motor proteins. Instead they mainly support and structure to maintain cell shape

  • anchors cell components

3) Microfiliments (Actin Filaments)

  • Polymer of actin proteins assemble in helical formation

  • ususally found underneath plasma membrane

  • provide structure, support & shape

    • they provide a specific shape for each cell

  • Actin filaments have one motor protein; myosin

    • function is intracellular transport;—→ cytoplasmic streaming

  • Specialized Structure-

    • Muscles: rely on myosin moving along actin filaments

Extracellular Matrix of Animal Cells

  • proteins (ex: collogen)

  • carbohydrates

  • proteins & carbohydrates attached are glycoproteins

  • Functions of Extracellular Matrix-

    • connects cells together. Cell/Cell communication

  • Cell Connections-

    • 2 cells physically connected with each other

    • In plants: plasamdesmata; tunnels connecting lytosols of two cells

Three Major Cell Connections

  • Tight Junction- zips 2 plasma membrans together

  • Desmosomes- disks of connection

  • Gap Junctions- tunnels connecting cytosols of 2 cells