Unit 2 - Cell Structure

STUDYING CELLS

  • microscope - an instrument that magnifies an object

  • light microscope - produce magnified images by focusing visible light rays

  • compound light microscope - allow light to pass through an image and use two lenses

  • nearly all living cells are transparent

            - use stains or dyes to solve this problem

            - now have fluorescence microscopy to identify location of molecules

  • electron microscope - produce magnified by focusing beams of electrons

  • can produce images almost 1000 times more detailed than light microscopes

  • 2 types

                - transmission: make it possible to explore cell structures and large protein molecules

                - scanning: produce three-dimensional images of the specimen’s surface


CELL THEORY

  • the cell theory:

  1. all living things are made of at least one cell

  2. the cell is the basic unit of life

  3. cells come from pre-existing cells

  • many individuals contributed to this


PROKARYOTIC CELLS

COMPONENTS OF PROKARYOTIC CELLS

  • all share 4 common components:

  1. plasma membrane

  2. cytoplasm

  3. DNA

  4. ribosomes

  • prokaryote - a simple, mostly single celled organism that lacks a nucleus

  • most have a peptidoglycan cell wall

  • capsule - enables the cell to attach to surfaces in its environment

  • flagella - used for locomotion

  • pili - used to exchange genetic material during conjugation



EUKARYOTIC CELLS

  • Things all eukaryotic cells have:

  1. membrane bound nucleus

  2. numerous membrane bound organelles

  3. several rod shaped chromosones

  • organelle - little organ

        - have specialized cellular functions

  • allow different functions to be compartmentalized in different areas


PLASMA MEMBRANE

  • plasma membrane - phospholpolipid bilayer with embedded proteins that seperates the internal contents of the cell from its surrounding environment

  • phospholipid - a lipid molecule with two fatty acid chains and a phosphate containing group

  • controls the passage of organic molecules, ions, water, and oxygen into and out of the cell

  • can be specialized in absorption

        - fingerlike projections called microvilli

        - lining of the stomach


THE CYTOPLASM

  • cytoplasm - the entire region of a cell between the plasma membrane and the nuclear envelope

  • made up of:

        - cytosol

        - organelles

        - cytoskeleton

        - various chemicals

  • consists of 70 to 80 percent water

  • has semi solid consistency

    - comes from proteins within cytoplasm

    - other organic molecules in the cytoplasm

        - glucose and other simple sugars

        - polysaccharides

        - amino acids

        - nucleic acids

        - and many others

  • many metabolic reactions take place in the cytoplasm

        - including protein synthesis


THE NUCLEUS

  • nucleus - houses the cell’s DNA and directs the synthesis of ribosomes and proteins

  • parts of the nucleus:

        - nuclear envelope

        - chromatin and chromosones

        - nucleolus


NUCLEAR ENVELOPE


  • double membrane structure that constitutes the outermost portion of the nucleus

  • both inner and outer membranes are phospholipid bilayers

  • contains pores that control the passage or ions, molecules, and RNA between the nucleoplasm and the cytoplasm


CHROMATIN AND CHROMOSOMES

  • chromosomes - structues within the nucleus that are made up of DNA

    - Eukaryotes - linear strucutes

    - Prokaryotes - circular

  • only visible from one another when the cell is getting ready to divide

  • chromatin - unwound protein chromosome complex

    - describes the material that makes up the chromosomes that both when condensed and decondensed


NUCLEOLUS

  • darkly stained area within the nucleus

  • aggregrates the ribosomal RNA with associated proteins to assemble the ribosomal subunits

  • ribosomal subunits are then transported out through the pores in the nuclear envelope to the cyptoplasm


RIBOSOMES

  • ribosomes - cellular organelles responsible for protein synthesis

  • may be free of attached

  • consist of two subunits

  • recieve their orders for protein synthesis from the nucleus where the DNA is transcribed into messenger RNA (mRNA)

  • mRNA travels to the ribosomes, which translates the code into a specific order of amino acids in a protein

  • are found in practically every cell

    - particularly abundant in cells that synthesize large amount of proteins


MITOCHONDRIA

  • energy factories of the cell

    - responsible for making ATP - the cells main energy carrying molecule

    - ATP represents the short term stored energy of the cell

  • mitochondria uses oxygen and glucose to produce energy in the form of ATP

  • muscle cells have a very high concentration of mitochondria

  • are oval shaped, double membrane organelles

  • have their own ribosomes and DNA

  • each membrane is a phospholipid bilayer embedded with proteins

        - the inner layer has folds called cristae

        - the area surrounded by the folds is called the mitochondrial matrix


PEROXISOMES

  • are small, round organelles enclosed by a single membrane

  • carry out oxidation reactions that break down fatty acids and amino acids

  • detoxify many poisons that may enter the body

        - alcohol is detoxified by peroxisomes in liver cells



VESICLES AND VACUOLES

  • membrane bounds sacs that function in storage (vacuoles) and transport (vesicles)

  • the membranes of vesicles can fuse with either the plasma membrane or other membrane systems within the cell


ANIMAL CELLS VS PLANT CELLS

  • differing structues


  1. centrosome - a microtubule-organizing center found new the nuclei of animal cells

contains 2 structures perpendicular to each other

replicates itself before a cell divides

appear to have some role in pulling the duplicated chromosomes to opposite ends of the dividing cell

  1. lysosome - the cells garbage disposal

enzymes within the lysosome aid in the breakdown of proteins, polysaccharides, lipids, nucleic acids, and worn out organelles

pH within lysosomes is more acidic than the pH of the cytoplasm

found in animal cells

  1. cell wall - rigid covering that protects the cell

also give structural support and gives shape to the cell

plant, fungal, and protistan cells have cell walls

major organic molecule in the plant cell wall is cellulose

  1. chloroplasts - plant cell organelles that carry out photosynthesis


ENDOSYMBIOSIS

  • mitochondria and chloroplasts contain DNA and ribosomes

  • symbiosis - two separate species depend on each other for their survival

  • endosymbiosis - mutually beneficial relationship in which one organisms lives inside the other



ENDOMEMBRANE SYSTEM

is a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins


ENDOPLASMIC RETICULUM

is a series of interconnected and membranous sacs and tubules that collectively modifies proteins and synthesizes lipids


ROUGH ER

transfer their newly synthesized proteins into the lumen of the RER where they undergo structural modifications


SMOOTH ER

synthesis of carbs, lipids, and steroid hormones

detoxification of medications and poisons

storage of calcium ions


GOLGI APPARATUS

sorts, tags, packages and distributes lipids and proteins

mail center


LYSOSOMES

  1. digestive component

  2. organelle recycling facility of animal cells

use their hydrolytic enzymes to destroy pathogens


CYTOSKELETON

  1. help maintain the shape of the cell

  2. secure some organelles in specific positions

  3. allow cytoplasm and vesicles to move within the cell

  4. enable cells within multicellular organisms to move

Three types: microfilaments, intermediate filaments, microtubles


MICROFILAMENTS

function in cellular movement


INTERMEDIATE FILAMENTS
function is purely structural


MICROTUBLES
1. help cell resist compression

  1. provide a track along which vesicles move through the cell

  2. pull replicated chromosomes to oppostie ends of a dividing cell