Cellular Components: The Nucleus

What makes up the nucleus structure?

• Nuclear envelope

• Nuclear pore complexes

• Nucleolus

What is the nuclear envelope?

• Forms the inner and outer membrane of the nucleus

• Outer membrane is continuous with the rER

What are the functions of nuclear pore complexes?

• Regulate movement of macromolecules in and out of the nucleus

• Allows for diffusion of small solutes

What is the nucleolus?

Region of the nucleus where ribosomes are formed

What type of ribosomes are formed in the nucleolus?

• DNA coding for rRNA

• rRNA

• Ribosomal proteins

• Newly formed ribosomal subunits

What cells are nucleolus more obviously seen?

Cells very active in protein synthesis

What are the various regions of DNA?

• ProteinCoding

• Non-coding

• Telomeres

What occurs in the protein coding regions of DNA?

• RNA transcription

What occurs in non-coding regions of DNA?

• Start of sequences

• Regulates gene expression

What are the telomere regions of DNA?

• Base pairs at the end of DNA strand

• Related to cell age

What is gene expression influenced by?

• Genetic regulators coded within the DNA

• Transcription factors (proteins)

• Other factors

What is epigenetics?

Changes in an organism caused by changes in gene expression not changes in genetic code

What are factors affecting epigenetics?

• Epigenetic factors such as changes in histone characteristics and methylation of DNA

• Environmental factors leading to epigenetic modifications that can be short or long lasting

What is methylation of DNA?

The altering of gene expression without altering the DNA sequence

What is the general cell cycle?

Interphase = G1 + Synthesis phase + G2

What is synthesis in terms of the cell cycle?

• Duplication of DNA and centrioles

• Requires the use of microtubules

Cell Response to environment

• Normal cell (homeostasis)

  • Stress: cell adaptation

    • Inability for cell to adapt leads to cell injury

  • Injurious stimulus: cell injury

    • Injury is mild: Reversible injury → cell returns to homeostasis

    • Injury is severe: Irreversible injury

      • Cell death occurs: Necrosis or Apoptosis

What are causes of cell damage?

• Ischemia: insufficient blood flow causing insufficient oxygen supply

• Infectious agents: bacteria, fungo, viruses

• Immune reactions: severe allergic reactions, autoimmune diseases

• Mechanical factors: physical injuries

• Chemical factors: heavy metals, drugs cytotoxic effects/side effects, excessive reactive oxygen species/free radicals

What is the tissue renewal process?

1. Mitosis

2. Replacement

3. Un-renewable

What occurs during mitosis during the tissue renewal process?

• Replication of self

• Ex: Liver

What occurs during replacement of the tissue renewal process?

• No mitosis

• Stem cells replace damaged or old tissue

• Progenitor cells replace damaged or old tissue

  • Muscle - satelite cells

  • Progenitor in periosteum: osteoblasts, chondroblasts

What are examples un-renewable cells in the tissues renewal process?

• Nerves

• Myocardium

What are examples of cell death?

• Apoptosis

• Necrosis

What is apoptosis?

Programmed cell death without an inflammatory reaction

What is necrosis?

Uncontrolled cell death inciting an inflammatory reaction

What occurs during apoptosis?

• Often physiological destruction of cells

  • Removal of unneeded cells or cells no longer functions

  • Tumor cells indicated by lymphocytes

  • Excessive cells (embyro)

• Pathogens can stimulate apoptosis

• Cancer cells can deactivate apoptosis

What occurs during necrosis?

• Cell experience morphological changes

  • Cells swell

  • Cell and organelle membranes are disrupted

    • Lysosome, perioxisomes, and proteasomes released

  • Contents of cell escape

• Causes an inflammatory response damaging other cells and tissues

  • Activates healing response

What are examples of cell/tissue adaptation?

• Hypertrophy

• Hyperplasia

• Atrophy

• Metaplasia

What is hypertrophy?

• Increased cell size

• Can be physiological such as in cardiac or skeletal muscle

• Can be pathological such as in cardiac muscle as well

What is hyperplasia?

• Increase in the number of cells

• Can be physiological such as callus on skin and bone marrow following blood loss

• Can be pathological such as pre-neoplastic (pre-cancerous) and benign prostatic hyperplasia

What occurs during atrophy?

• Decrease in cell size

• Can be physiological such as in the thymus and uterus after parturition

• Can be pathological such as in decreased work load, diminished blood supply, malnutrition, reduced endocrine stimulation, denervation

What occurs during metaplasia?

• Reversible changes in cell types

• Such as changes in bronchial epithelium cells of a smokers

• If stimulus for change persists it can lead to a malignant irreversible change in cell types