Week 2/2-2/9

Lecture 2/3

Exam 1 - Feb 19

Exam 2 - Mar 19

Exam 3 - Apr 23

Final Exam - May 19

NO DROPPING OF ANY EXAMS

Cell Structure

  • How do they form?

  • What are they used for?

  • What are they made from

  • How are they positioned in the cell?

  • Answers & ideas:

    • Expanded and shrinked

    • Change in shape when engulfing things

    • Tearing away, latching on

    • Looking like it was seeking something, reeled it in (called questing)

    • What kind of structure provides these forces such as bending?

What are cells made of?

  • DNA/RNA*

  • Nucleic acids*

  • Protein/amino acids*

  • H2O

  • Carbs*

  • Lipids*

  • Glucose

  • Oxygen

DO NOT USE PROKARYOTE IN THIS CLASS

Cellular Components

  • Membranes

  • Cell wall

  • Cytosplasm

  • Vacuoles

  • Membrane-bound compartments

  • Cytoskeleton

What are the differences between eukaryotes and bacteria/archaea?

  • Bacteria/archaea have organelles!

  • Main things present in eukaryotes:

    • Nucleus

    • Golgi

    • ER

    • Peroxisomes

    • Actin, myosin, tubulin

    • Mitochondria

The Bacterial Cell: An Overview

  • Cytoplasm - consists of a gel-like network

  • Cell membrane - encloses the cytoplasm

  • Cell wall - covers the outside of the cell membrane

  • Nucleoid - non-membrane bound area of the cytoplasm that vonysind the chromosome in the form of looped coils

  • Flagellum - external helical filament whose rotary motor propels the cell

    • Not evolutionary related to each other

The Bacterial Cell

  • Cytoplasm surrounded by envelope

    • Cytoplasm contains DNA in nucleoid

  • Envelope has lipid membrane boundary plus a structural cell wall

  • GM+ → 1 membrane

  • GM- →2 membranes (outer + inner)

What are the major functions of the Cytoplasmic Membrane?

  • Structure & shape - what properties provide this?

    • Channels

    • Membrane made from - lipids

      • Water has trouble getting in the membrane

      • Ions as well

      • Anything large, charged, or polar

      • To create a semipermeable layer

  • Permeability barrier - prevents leakage and functions as a gateway for transport of nutrients into and out of the cell

  • Protein anchor - site of many proteins involved in transport, bioenergetics, and chemotaxis

  • Energy conservation - site of generation and use of the proton motive force

Cell membranes

  • Made of lipid bilayer

  • Separate the cytoplasm from the outside world

  • Some proteins are embedded in membrane

    • Anchor membranes to envelope

    • Sense the outside world

    • Transport materials into and out of cell

Membrane Lipids

  • Membranes have equal volumes of phospholipids and proteins

  • Phospholipid - consists of glycerol wit ester links to two fatty acids and a phosphoryl head group

  • The two layers are called leaflets

Diverse Membrane Lipids

  • Unsaturated chains

Bacteria/Eukaryotes have different membrane lipids than Archaea

  • Bacteria/Eukaryotes

    • Ester-linked lipids

    • Lipids are fatty acids

  • Archaea

    • Ether-linked lipids

    • Lipids are branched terpenoids

  • Called the Great Lipid Switch due to this difference in lipids

Archaeal lipids

  • The # of rings in the lipid increases with the growth temperature

  • Using lipids with higher rigidity prevents the membrane from “melting” at higher temperatures

  • Think of butter, when it’s solid in cold temperatures but becomes a liquid in hot temperatures

Membrane Structure of Bacteria & Archaea

  • Bacteria

    • Phospholipid - bilayer

  • Archaea

    • Phospholipid - monolayer

Different means of adding membrane rigidity

  • Bacteria & eukaryotes

    • Cholesterol - eukaryotes

    • Hopane - bacteria

  • Archaea

    • Branched lipid ether - rings?

Membrane Proteins

  • Membrane proteins serve numerous functions, including:

    • Structural support

    • Detection of environmental signals

    • Secretion of virulence factors and communication signals

    • Ion transport and energy storage

  • Membrane proteins often contain both hydrophilic and hydrophobic regions, allowing them to be inserted into the cell membrane.

Transport across the cell membrane

  • The cell membrane acts as a semi-permeable barrier

  • Selective transport is essential for survival

    • Small unchanged molecules, easily permeate the membrane by passive diffusion

  • Some molecules will diffuse passively through the membrane following concentration gradients

  • Others require energy to be transported against the concentration gradient

Transport of most solutes occurs faster than diffusion

  • Transport is an active process

  • Requires energy

  • Often occurs against a concentration gradient

  • Highly specific

  • Shows saturation effect (finite concentration of the carrier)

  • Biosynthesis of transporters is often regulated by the cell

  • Limit is the # of transporters

Transport systems

  • There are 3 modes of transport:

    • Uniporter - one way in

    • Antiporter - opposite directions

    • Symporter - same directions

    • Coupling the simultaneous transport of different molecules allows the cell to use chemical gradients as a source of energy

3.1 - The Bacterial Cell: An Overview

Bacteria share these traits:

  • Thick, complex outer envelope

  • Compact genome

  • Tightly coordinated functions

Cytoplasm

  • Contained by a cell membrane or plasma membrane

    • Plasma membrane is also known as the inner membrane which is composed of phospholipids

  • Periplasm - water-filled space containing nutrient-binding proteins and secretion machines

  • Outside the cell wall is the lipopolysaccharides (LPS)

    • Class of lipids attached to long polysaccharides (sugar chains)

    • Form a slippery layer that inhibits phagocytosis

  • Envelope - cell-surface proteins that enable the bacterium to interact with specific host organisms

Bacterial Cell Membrane

Steps:

  • ATP synthase causes the flow of H+ ions

  • Flow of H+ ions is driven by the charge difference and concentration difference

  • This is considered a “molecular machine”

  • Nucleoid - chromosome organized within the cytoplasm as a system of looped coils

Small Molecules and Ions

  • Inorganic ions - ions that store energy in the form of transmembrane gradients + serve essential roles in enzymes

  • Small charged organic molecules

    • Polyamines - molecules with multiple amine groups that are positively charged when the pH is near neutral

Macromolecules

  • Electrophoresis - negatively charged molecules migrate in an electrical field

    • DNA and RNA can be isolated using this method

  • Proteome - proteins express by a cell under given conditions

  • Peptidoglycan - an organic polymer of peptide-linked sugars that constitutes nearly 1% of the cell mass

Cell Tractionation - how we separate cell components such as membranes, ribosomes, and flagella

  • Also provides purified proteins that act as antigens for candidates vaccines

  • Steps to fractionation of Gram-negative cells:

    1. EDTA weakens outer membrane, and sucrose enters periplasm

    2. Lysozyme breaks down cell wall, causing spheroplast formation

    3. Water dilution shocks outer membrane; periplasm leaks out

    4. Ultracentrifuge

    5. French press

    6. Ultracentrifuge

    7. Density gradient ultracentrifugation

Spheroplast - lacking the turgid cell wall, the cell swells into a sphere

Ultracentrifuge - a device in which tubes containing solutions of cell components are spun at very high speed

To summarize:

  • Bacterial cells are protected by a thick cell envelope

  • A Gram-negative cell includes an outer membrane

  • Bacteria are composed of nucleic acids, proteins, phospholipids, and other organic and inorganic chemicals

  • The bacterial cytoplasm is highly structured

  • Cell fractionation isolates cell parts for structural and biochemical analysis

  • Cell compartments contain different types of proteins

  • Microscopy reveals cell structure