MCAT Biology Review: Parts of the Cell and Reproduction

Parts of the Cell

  • Nucleoid:
    • The region in prokaryotes where DNA is located.
    • Prokaryotes lack a nucleus.
  • Nucleolus:
    • Found within the nucleus of eukaryotes.
    • Does not have a membrane.
    • Responsible for making ribosomes.
  • Ribosomes:
    • Essential for connecting amino acids to form the primary protein chain.
    • Present in both prokaryotes and eukaryotes.
  • Peroxisomes:
    • Break down materials, including waste and dangerous substances.
  • Rough Endoplasmic Reticulum (ER):
    • Accepts mRNA to synthesize proteins.
    • Studded with ribosomes, hence the "rough" appearance.
  • Smooth Endoplasmic Reticulum (ER):
    • Involved in detoxification and lipid synthesis.
  • Golgi Apparatus:
    • Modifies and distributes proteins.
    • Found only in eukaryotes.
    • Functions as the cell's packaging system.
    • Cis Side: Faces the nucleus.
    • Trans Side: Faces the plasma membrane.
    • COP I: Vesicles transport from the Golgi back to the ER (retrograde).
    • COP II: Vesicles transport from the ER to the Golgi (anterograde).
    • Clathrin: Vesicles transport between the plasma membrane and Golgi apparatus.
  • Centrioles:
    • Consist of nine groups of microtubules.
    • Two centrioles are arranged at right angles to form a centrosome.
    • Centrosomes play a crucial role in separating chromosomes during anaphase.
  • Lysosomes:
    • Serve as the recycling center of the cell.
    • Produced by the Golgi apparatus and have a single membrane.
  • Plasmids:
    • Found in prokaryotes.
    • Carry DNA that is not essential for survival but can provide advantages.
    • Circular DNA that can replicate rapidly.

Bacterial Shapes

  • Bacilli: Rod-shaped bacteria.
  • Cocci: Spherical-shaped bacteria.
  • Spirilla: Spiral-shaped bacteria.

Anaerobes

  • Obligate Aerobes: Require oxygen to survive.
  • Obligate Anaerobes: Cannot survive in the presence of oxygen.
  • Facultative Anaerobes: Can switch between aerobic and anaerobic conditions.
  • Aerotolerant Anaerobes: Do not use oxygen but are not harmed by its presence.

Gram Staining

  • Purple: Indicates a thick peptidoglycan cell wall.
  • Pink: Indicates a thin peptidoglycan cell wall and an outer membrane.

Eukaryotes vs. Prokaryotes

  • Eukaryotes:
    • Electron transport chain (ETC) in the mitochondria.
    • Large ribosomes.
    • Reproduce via mitosis.
  • Prokaryotes:
    • ETC in the cell membrane.
    • Small ribosomes.
    • Reproduce via binary fission.
    • Plasmids carry DNA and virulence factors.
    • Plasmids can integrate into the genome, forming episomes.

Miscellaneous

  • Prions:
    • Infectious proteins that trigger misfolding of other proteins.
    • Responsible for diseases like mad cow disease.
  • Vireoids: Plant pathogens.

Cytoskeleton

  • Microfilaments:
    • Smallest filaments.
    • Actin is a key component.
    • Important for cell motility and contraction.
  • Microtubules:
    • Largest filaments.
    • Tubulin is a key component.
    • Important in centrioles and centrosomes for moving things within the cell.
  • Intermediate Filaments:
    • Intermediate in size.
    • Keratin and desmin are important examples found in nails and hair.
    • Provide structural support.

Tissues

  • Epithelium:
    • Covers the outer layer of the body surface or a hollow structure.
    • Thin tissue forming the outer layer of a body surface or organ.
    • Parenchyma: The functional part of an organ.
    • Simple: One layer of cells.
    • Stratified: Multiple layers of cells.
    • Pseudostratified: Appears to have multiple layers but is a single layer with varying cell sizes.
    • Cuboidal: Cube-shaped cells.
    • Columnar: Column-shaped cells.
    • Squamous: Flat cells.
  • Connective Tissue:
    • Supports, protects, and provides structure to other tissues and organs.
    • Found in the extracellular matrix.
    • Stroma: Provides support in the extracellular matrix.
    • Important in bone, cartilage, tendon, and blood.

Genetic Recombination in Bacteria

  • Transformation: Bacteria take up genetic information from the environment.
  • Conjugation:
    • Transfer of genetic information via a conjugation bridge (like bacterial sex).
    • Allows bacteria to exchange DNA, such as antibiotic resistance genes.
  • Transduction: Transfer of DNA using a bacteriophage (bacteria-specific virus).
  • Transposons: Genetic sequences that can insert and remove themselves from DNA.

Viruses

  • Capsid: The protein coat of a virus.
  • Envelope: Some viruses have this outer layer.
  • Virions: Individual virus particles.
  • Bacteriophages: Viruses that infect bacteria.
  • Viral DNA/RNA:
    • Can be DNA or RNA.
    • Can be single-stranded or double-stranded.
    • Positive-sense RNA: Can be directly translated into proteins in the host cell.
    • Negative-sense RNA: Requires RNA replicase to convert it to a complementary strand before translation.
  • Retroviruses:
    • Single-stranded RNA viruses.
    • Use reverse transcriptase to convert RNA into DNA, then back into RNA and proteins.
  • Bacteriophages (Lytic vs. Lysogenic):
    • Lytic: Virions are made until the cell bursts.
    • Lysogenic: Virus remains dormant until stress activates it, then enters the lytic phase.

Reproduction: Cell Cycle

  • Most of the cell cycle is interphase.
  • Mitosis is the process of cell division where one parent cell makes two daughter cells.
  • $\text{G1}$ phase: the cell is making mRNA and proteins.