Cells Study Notes

Cytoplasm

  • Definition: A jelly-like fluid inside the cell in which the organelles are suspended.

Cytoskeleton

  • Definition: A network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement.

Centrosome

  • Definition: Microtubule organizing center.

Centrioles

  • Definition: Cell organelle that aids in cell division in animal cells only.

Nucleus

  • Definition: A part of the cell containing DNA; it is regarded as the control center of the cell.

Nucleolus

  • Definition: A small dark staining body inside the nucleus; produces ribosomes (rRNA).

Rough Endoplasmic Reticulum (RER)

  • Structure: Has many ribosomes attached.

  • Function: Processes and transports proteins.

Nuclear Membrane/Envelope

  • Structure: Composed of a lipid bilayer.

  • Function: Controls what enters and leaves the nucleus through the pores.

Ribosome

  • Definition: Organelle that makes proteins; where TRANSLATION occurs.

Smooth Endoplasmic Reticulum (SER)

  • Structure: Further from the nucleus than the RER; no ribosomes attached.

  • Functions:

    • Synthesis of lipids, fatty acids, and carbohydrates.

    • Detoxification of drugs.

Golgi Apparatus/Body

  • Analogy: Comparable to FedEx or a shipping center.

  • Function: Packages products of RER and SER for internal use or export to blood.

Vesicle

  • Definition: A small membrane-bound sac that transports substances in and out of cells.

Lysosomes

  • Definition: An organelle containing digestive enzymes; digests worn out organelles and debris.

Peroxisomes

  • Definition: Organelles that contain oxidase enzymes that detoxify alcohol, hydrogen peroxide, and other harmful chemicals.

  • Note: Many of these are found in the liver.

Mitochondria

  • Definition: Known as the powerhouse of the cell; organelle that makes ATP via aerobic cellular respiration.

Cell Cycle

  • Overview: The various phases through which a cell goes during its life.

  • Key Phases:

    • G1 Phase: Cell growth (Gap 1).

    • S Phase: The synthesis phase of the cell cycle; DNA is replicated.

    • G2 Phase: Gap 2; growth phase that prepares for division, includes CHECKPOINTS for division.

Apoptosis

  • Definition: Programmed cell death; occurs when a cell fails checkpoints in the cell cycle and self-destructs.

Cancer

  • Definition: Uncontrolled cell division and growth.

  • Causal Factor: Occurs if a cell has some faulty growth or DNA replication but the checkpoints in the cell cycle fail to detect these errors.

DNA Transcription

  • Definition: The process of making a template; mRNA makes a template/copy of DNA in the nucleus.

Translation

  • Definition: The process that occurs in ribosomes in the cytoplasm; ribosomes "read" the mRNA and translate it into a string of amino acids (a protein).

Key Enzymes

  • DNA Polymerase: Enzyme that forms the new strands during DNA replication by adding new nucleotides in the correct order.

  • RNA Polymerase: Enzyme that forms the new strands during transcription; forms mRNA by adding new nucleotides in the correct order.

Synthesis of RNA

  • Transcription: Synthesis of an RNA molecule from a DNA template (occurs in the nucleus).

  • Translation: Happens in the cytoplasm by ribosomes; the process by which mRNA is decoded and a protein is produced.

Mitosis

  • Definition: The division of the nucleus (and usually the whole cell); it makes an exact copy of the cell.

  • Chromosome Count: The cell is diploid (has 46 chromosomes).

Meiosis

  • Definition: A reduction division that forms eggs and sperm; produces unique haploid cells.

  • Chromosome Count: The cell has 23 chromosomes.

Cell Junctions

  • Gap Junction: Allows ions and small molecules to pass directly from one cell to another.

  • Desmosome: A circular-shaped cell junction that tightly joins adjacent cells together.

  • Hemidesmosome: Anchors cells to tissue below (basement membrane).