AA

BIOL 215 Lecture 4

The Sedimentation Coeffecient

  • Sedimentation coefficient: measures how rapidly a particle sediments under the centrifugal force
    • higher sedimentation coefficients mean the particle settles more rapidly
  • We use the sedimentation coefficient to see which structures will sediment first

Prokaryotic Subcellular Structures

Cytoplasm

  • The cytoplasm consists of the cytosol and subcellular structures
    • Cytosol: gel-like semifluid material inside cells that suspends the particles inside the cell

Plasma Membrane

  • The plasma membrane is 4-8 nm thick
  • It is made of phospholipids and proteins
  • The functions of the plasma membrane include:
    • serving as a boundary between the cell and external environment
    • regulating the movement of particles in and out of a cell
    • mediating communication with the external environment

Ribosomes

  • Ribosomes are responsible for protein synthesis
  • They are a type of ribonucleoprotein complex
    • Ribonucleoprotein complex: any particle made out of RNA and proteins
  • Sedimentation coefficients for the ribosome and its parts:
    • The full ribosome is 70S
    • The small subunit is 30S
    • The large subunit is 50S
  • Some antibiotics can inhibit prokaryotic ribosome activity to kill bacteria
    • This doesn’t affect human cells because eukaryotic ribosomes are bigger than prokaryotic ribosomes.

Nucleoid Region

  • Nucleoid region: the area in the cytoplasm of prokaryotes where the DNA is located
    • This area is not enclosed

Cell Wall

  • Peptidoglycan: a polymer made of chains of NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine) that are cross-linked together by peptide chains
    • This is what makes up the cell walls of bacteria
    • Some antibiotics interfere with the synthesis of peptidoglycan to kill bacteria
    • This doesn’t affect human cells because they do not have peptidoglycan cell walls
  • Pseudomurein: a polymer made of chains of NAT (N-acetyltalosaminuronic acid) and NAG (N-acetylglucosamine) that are cross-linked together by peptide chains
    • This is what makes up the cell walls of archaea
  • Archaean cell walls tend to be more proteinaceous than bacterial cell walls

Eukaryotic Subcellular Structures

Plasma Membrane

  • Refer to the section in “Prokaryotic Subcellular Structures” on the plasma membrane

Cytoplasm

  • The cytoplasm consists of cytosol, organelles, and other subcellular structures
    • Organelles: membrane-bound subcellular structures with specific functions in eukaryotes

Extracellular matrix

  • Extracellular matrix: a fibrous network outside of the cell that the cell is tethered to
  • Components of the extracellular matrix are generally made of different proteins and/or polysaccharides
    • This can vary depending on the cell type
  • The extracellular matrix is linked to cells via components on the cell membrane
  • Functions of the extracellular matrix:
    • Support/structure
    • Adhesion to the surrounding medium

Nucleus

  • The main function of the nucleus is to store DNA
  • Structure of the nucleus:
    • 5-6 micrometers in diameter
    • Nuclear envelope: a double-layered membrane that surrounds the nucleus
    • Nuclear lamina: a network of intermediate filaments beneath the inner layer of the nuclear envelope
    • This may also play a role in chromatin organization
    • Nuclear pores: regulated openings through the nuclear envelope that control the movement of substances in and out of the nucleus
    • Each pore is controlled by a nuclear pore complex
    • Nucleolus: clustered regions of genes for rRNA surrounded by specific RNAs and proteins
    • this is the site of ribosomal subunit synthesis

Ribosomes

  • Still the site of protein synthesis
  • The sedimentation coefficients are bigger for each part:
    • The full ribosome is 80S
    • The small subunit is 40S
    • The large subunit is 60S

Rough Endoplasmic Reticulum (RER)

  • Rough endoplasmic reticulum: large flattened membrane sheets that temporarily house ribosomes
  • The function of the RER is to produce proteins and glycoproteins
    • These are then delivered to other parts of the endomembrane system by transport vesicles

Smooth Endoplasmic Reticulum (SER)

  • SER looks like RER but without ribosomes
  • It is continuous with the RER
  • Functions of SER include:
    • lipid synthesis
    • carbohydrate metabolism
    • storing calcium ions
    • detoxifying poisons

Golgi Apparatus

  • Structure of the Golgi apparatus:
    • It is a system of flattened membranous sacs
    • Cis Golgi network: the side of the Golgi apparatus closer to the endoplasmic reticulum
    • Trans Golgi network: the side of the Golgi apparatus closer to the plasma membrane

Gram Stain

  • Gram stain: a technique used to identify bacteria based on characteristics of their cell wall
  • Steps of the gram stain:
    • Cells are stained with a purple dye
    • They are rinsed with alcohol
    • Then they are stained with a red or pink counterstain
  • Gram-positive bacteria appear to be purple
    • This is because the purple dye passes through the peptidoglycan and goes into the cytoplasm
    • Gram-positive bacteria have a thick layer of peptidoglycan
  • Gram-negative bacteria appear to be pink
    • This is because the alcohol rinse washes the purple dye out of the top peptidoglycan layer, allowing the pink dye to enter
    • Gram-negative bacteria have an outer membrane and then a thin layer of peptidoglycan around their plasma membrane