Ch. 4: Cells, Membrane & Membrane Proteins, Protein Production

Things to Know

You should have an understanding of the following:

1. Review cell structures and their basic functions.

2. Nucleus:

         A) DNA, nucleolus, nuclear pores

3. Mitochondria:

A) Internal structures

Contains own DNA → self-replication and protein synthesis

B) Make the connection to what you learned about cellular respiration from Ch. 3 and this organelle.

Mitochondria is the powerhouse of the cell; site of Intermediate Step, Krebs/Citric Acid Cycle, and ETC

4. Membranes:

A) Be able to describe the structure of a membrane (fluid mosaic model). How do phospholipids contribute to the characteristics of the membrane?

Phospholipids are the ‘sea’ and the proteins are the ‘icebergs’

B) What are the functions of the various membrane proteins?

  • Transport protein

    • Channel (leak)

      • Generally stay open, but can close

    • Carrier

      • Requires ATP to open

  • ID markers/Recognition

  • Cell Receptor Surfaces/ligands

  • Anchoring Sites

  • Cell Adhesion

  • Enzymes

5. Transport:

A) Differentiate between active and passive transport through a cell membrane.

  • Active

    • Req’s ATP to move against concen gradient (low → high)

  • Passive

    • No ATP req’d

B) What is the difference between simple diffusion, osmosis and facilitated diffusion?

  • Simple diffusion

    • Substances have their own concen gradient

    • Ions run along electrical gradients

    • Molecules must be small and have no electrical charge

  • Osmosis

    • Diffusion of water through a selectively permeable membrane

  • Facilitated Diffusion

    • Diffusion of a molecule with the help of a

      • Channel protein: ions

      • Carrier protein: small polar molecules

        • Polar = hydrophilic, meaning they can’t easily pass through phospholipid bilayer

C) What is meant by concentration gradient?

How the concentration of substances change over time (high → low = passive; low → high = active)

D) Tonicity: isotonic, hypertonic and hypotonic; crenation, hemolysis

Isotonic = same tonicity; no net movement

Hypertonic = one solution is more concentrated than the other; water follows solution with more solute; if ECF is more hypertonic than ICF, cell may crenate

Hypotonic = one solution is less concentrated than the other; water follows solution with more solute; if ECF is more hypotonic than ICF, cell may hemolyze

E) Know what exocytosis and endocytosis are. Know terms phagocytosis and pinocytosis.

Exocytosis — vesicle released out of cell

  • Fuses w/ membrane

Endocytosis — vesicle formation

  • Moves into cell

  • Phagocytosis = ingestion of substances

  • Pinocytosis = ingestion of liquid

Cells

  • The Cell Theory

    • Cells are the basic unit of life

    • Building blocks of the human body

    • All organisms are composed of cells

    • New cells are derived from existing cells

  • Common Characteristics of Cells

    • All cells perform the general functions necessary to sustain life

      • Divided by functions (skin cells will do one thing, heart cells will do other things, etc.)

    • Cells vary in shape

    • Cells vary in size

      • Leleimited due to transport

        • Choice is to die or divide

          • Some cells are amitotic


  • Plasma (Cell) Membrane

    • Forms the outer barrier

    • Phospholipids and proteins

    • Semi-permeable


  • Cytoplasm

    • Cellular contents located between the plasma membrane and the nucleus

    • Organelles

    • Cytosol

      • Jelly-like fluid that fills inside of a cell

    • Cytoskeleton

  • Nucleus

    • Cell’s control center

    • Controls protein synthesis

    • Nuclear envelope w/ pores, nucleolus (ribosomes), chromatin, and chromosomes

      • Nuclear envelope is around the nucleus

    • Ribosomes are responsible for protein production (transcription & translation); associated w/ RER

      • Each ribosome has a small and a large subunit

      • They exit from the nucleus via the nuclear pores


  • Organelles

    • Each type of organelle performs a different function for the cell

    • Collectively, the specialized functions of all organelles are essential for normal cellular structure and activities

    • Mitochondria

      • ~powerhouse of the cell~

      • Produce large amounts of ATP (cellular respiration)

      • Double-membrane

      • Contains own DNA: self-replication & protein synthesis

    • Endoplasmic Reticulum

      • Synthesis of lipids, proteins, storage, and transport

      • Rough ER — ribosomes make proteins; granular appearance

        • Closest to nucleus

      • Smooth ER — synthesis of lipids; smooth, tubular appearance

        • Further from nucleus


    • Golgi Apparatus

      • “FedEx of the cell”

      • Modifies & repackages proteins and lipids as vesicles

      • Can make glycoproteins, lipoproteins

      • Flattened stack of pancakes



    • Vesicles

      • Membrane-bound sacs produced by many organelles to transport products throughout the cell

      • Lysosomes, peroxisomes

        • Helps clean out waste

    • Cytoskeleton

      • Filamentous proteins which helps give the cell its shape and coordinates cellular movements

        • Microfilaments

        • Intermediate filaments

        • Microtubules

    • Cilia & Flagella

      • Appendages extending from the surface of some cells

      • Cilia work together to move materials or fluids along the surface of a cell (ex. respiratory cells)

      • Flagella act like a whip-like tail (ex. sperm)


    • Cell-to-Cell Junctions

      • Tight junctions

        • So tightly held together, nothing can get in between the membrane of one cell and another

        • Very common

      • Adherens junctions

        • Keeps cells close together, but allows for some stretch

      • Gap junctions

        • Little channels between two membranes

        • Allows stuff to pass through from one cell to another


      • Desmosomes

        • Don’t allow for any stretch

        • Will allow some passage in between


  • Brief Overview of Cell Cycle

    • New cells must be made continuously in order for an organism to grow and replace its damaged cells

    • Mitosis (somatic cells) & cytokinesis

      • Phases: Interphase, prophase, metaphase, anaphase, telophase

        • Interphase — steady state of cell

          • G1 Phase: making enzymes for next step

          • S Phase: DNA replication and growth; will be in chromatin state

          • G2 Phase: Makes enzymes to be used in mitosis (PMAT)

          • No need to memorize G/S phases

        • Prophase: chromatin → chromosomes

        • Metaphase: lines up chromosomes at equatorial plate

          • Centrioles are poles

        • Anaphase: pulls chromosomes apart via centrioles

        • Telophase: Pinching of cytoplasmic membrane (cytokinesis); chromosomes decondense back into chromatin

      • Review the basics of what occurs in each phase



    • Meiosis (sex cells) & cytokinesis

      • Diploid → haploid

      • 2 parent cell → 4 daughter cells

      • 2 sets of phases: Meiosis I and Meiosis II

      • Review the basics of what occurs in each phase




Membrane & Membrane Proteins

  • The lipid bilayer gives the membrane it flexible and fluid characteristics

    • The membrane is self-healing when punctured

    • When vesicles fuse w/ membrane (exocytosis)

    • When bits of membrane pinch off and become vesicles (endocytosis)

    • Fluid Mosaic Model (def gonna be on test in some fashion)

      • “Protein icebergs floating in a sea of lipids'“

      • Fluid: lipids (phospholipids and cholesterol)

      • Mosaic: many different proteins

        • Peripheral and integral proteins

  • Membrane Proteins

    • Transport proteins

      • Channel (leak)

        • Generally stay open, but can close

      • Carrier

        • Typically needs ATP to open up

    • Identity markers/Recognition

    • Cell surface receptors/Ligands

    • Anchoring sites

    • Cell adhesion

    • Enzymes

  • Channel-mediated diffusion

    • Certain small water-soluble molecules can pass through

      • Non-water soluble (lipids) don’t need a protein; can just pass on through phospholipid bilayer

    • Specific to what it allows to pass through

      • Selective due to charge of molecule and channel protein

    • High → low concen


  • Carrier proteins

    • Can move larger molecules across the membrane by changing shape

    • Carrier proteins change shape to transport molecules across the plasma membrane

    • Specific shape for certain molecules or ions


  • Transport Through the Membrane


    • Lipid: can pass right thru phospholipid

    • Lipid: can pass right thru phospholipid

    • Water: needs a carrier protein (can’t pass through phospholipid)

    • Active: requires ATP to move against concen gradient (low → high)

  • Passive Transport - no ATP

    • Simple diffusion

      • Each substance has its own concentration gradient

      • Ions run along electrical gradients

      • Through the lipid bilayer: molecules must be small w/ no electrical charge



    • Osmosis

      • Diffusion of water through a selectively permeable membrane

      • Most water molecules pass through special channels called aquaporins

      • A few water molecules can slip through the lipid bilayer

      • Osmotic pressure — pressure exerted by the mvmt of water across a semipermeable membrane

        • Caused by different in water concentration

        • The steeper the gradient, the greater the amount of water moved and the higher the osmotic pressure

          • 0.9% cell, 10% Na solution (extremely hypertonic, water moves out readily)

          • 0.9% cell, 1% Na solution (barely hypertonic; some water movement to outside, but not alot)

    • Facilitated diffusion (channel and carrier mediated)

      • Diffusion of a molecule with the help of a

        • Channel protein: used by ions

          • Ions are smaller; can kinda meander their way through

        • Carrier Protein: used by small polar molecules

          • Typically larger; need carriers

      • Passive, no energy required


  • Active Transport

    • Moves particles from low to high concen, against concen gradient

    • Requires ATP

    • Uses carrier proteins

    • Ex. Sodium-Potassium pump (3 Na go out : 2 K go in)


      • Goes back and forth; take notice of the shape in protein


      • Pumping out 3 Na every time you change the shape


      • ATP drops off phosphate; drops off 3 Na; phosphate drops off; 2 K can come in;

    • Primary v. Secondary

  • Primary Active Transport

    • A carrier protein uses energy from ATP to pump molecules across a membrane AGAINST (up) their concen gradient

    • Ex. Calcium pump (an ion pump)




  • Secondary Active Transport

    • Involved 2 different substances

    • Ones moves w/ (down) its concen gradient through a channel protein (passive transport)

    • The flow of the 1st substance powers the pumping of a 2nd substance through the same channel protein (active transport)

    • The 2nd substance is moving against (up) its concen gradient

    • The energy for active transport here is not from ATP; it’s the kinetic energy from the flow of the 1st substance that powers the pump

    • Types

      • Symporter: substances move in the same direction

        • Even though they’re moving in the same direction, one is still powering the other

      • Antiporter: substances move in opposite directions

        • as

  • Vesicular Transport (a form of active transport)

    • Endocytosis — vesicle formation

      • Phagocytosis, pinocytosis


    • Exocytosis — vesicle release out of cell

      • Can inc cell membrane





Protein Production

  • RNA & Protein Synthesis

    • DNA contains all the info needed to make proteins

    • RNA acts as intermediary and can be used over and over to make the same type of protein

  • Ribonucleic Acid (RNA)

    • 3 parts

      • Sugar = ribose

      • Phosphate group

      • Nitrogenous base (4)

        • Adenine (A)

        • Guanine (G)

        • Cytosine (C)

        • Uracil (U)

      • Complimentary strands follow same base pair rule, except U replaces T (A-U)

    • Purines & pyrimidines

    • 3 types of RNA

      • mRNA (messenger)

      • rRNA (ribosomal)

      • tRNA (transfer)

  • Stages of Protein Synthesis

    • 2 stages

      • Transcription — assemble RNA from DNA template

      • Translation — RNA and ribosomes assemble amino acids into a long chain protein

  • Transcription

    • Takes place in the nucleus

    • DNA unzips and one strand acts as template for making RNA

    • RNA polymerase assembles nucleotide bases to region of DNA template

    • Starts at a promoter site that signals RNA growth, DNA sections are called triplets

    • RNA grows, then detaches from DNA and DNA re-zips

    • RNA is modified by snipping out unnecessary sections & RNA leaves the nucleus

  • Translation

    • Takes place in the cytoplasm in 3 parts

      • Nuclear pores allow ribosomes to come out

      • Initiation — strand of mRNA attaches to two ribosomal units to make complex

        • rRNA will be helping by ‘taping’ ribosome complex together

        • Start codon (AUG) is the start point

        • P and A sites, tRNA (anticodon)

          • Brings complimentary base

      • Elongation — complex slides over mRNA while tRNA brings in amino acids, making a long chain polypeptide

      • Termination — stop codon reached and protein synthesis is finished; complex fall apart

    • mRNA & tRNA can be used repeatedly, protein goes off


  • Mutations

    • Can occur in either DNA or RNA

    • Can be caused by mutagens, accidental exposures, or spontaneously

    • Can cause no effect, be harmful, or cause the protein to not be made

    • Types

      • Base pair substitution (point mutation)

      • Frame shift mutations