The Cell: Anatomy and Division

• Anatomy of the Cell:-nucleus-plasma membrane-cytoplasm-organelles-cell specializations (cilia, flagella)

• Relationship between cell structure and function

• Cell division: mitosis and cytokinesis

The Plasma Membrane

The cell wall (or plasma membrane) has several functions:• provides structural support to the cell

• provides a protective barrier to the cell, limiting entry of extracellular elements

• involved in cell-cell interactions and cell signaling (ion channels, receptors)

• maintains resting potential: difference in electrical charge inside and outside of the cell. Important for function of excitable cells, such as neurons and muscle cells.

The Cell Nucleus

• The nucleus contains the genetic material (DNA) of the cell.

DNA RNA PROTEIN

• In the nondividing cell, DNA is in an uncoiled, dispersed state, and is referred to as chromatin.

• When the cell is about to divide, the DNA coils and condenses into chromosomes.

• The nucleus is required for cell division and RNA synthesis.

• The nucleus has a nuclear membrane, which separates contents of nucleus from cytoplasm.• The nuclear membrane has pores, which allows the passage of RNA and proteins.• The nucleolus is the site of ribosome synthesis.

The Cell Nucleus

PlasmaMembrane

Nucleus

Nucleolus

Cytoplasm

Mitochondria: Powerhouse of the Cell

• Composed of inner and outer membrane.• Inner membrane has infoldings called cristae.• The space formed by the inner membrane is the

mitochondrial matrix.• Enzyme reactions in the inner membrane and

matrix result in ATP production (stay tuned!)• Very abundant in cells which use a lot of energy.

Ribosomes

• Sites of protein synthesis.• Composed of two subunits,

made of rRNA and proteins.• Assembled in the nucleolus,

moves to cytoplasm.• Found free or attached to

endoplasmic reticulum (ER).

Endoplasmic Reticulum• Series of interconnecting membranous

tubules.• Interior spaces of the ER are called the

cisternae.• The rough ER has attached ribosomes:

site of protein synthesis.• The smooth ER lacks ribosomes: site of

lipid production, detoxification of chemicals and drugs.

Golgi Apparatus

• Composed of stacked, flattened membranous sacs with cisternae.

• Role in modification and packaging of proteins and lipids for transport.

• Numerous in cells which secrete lots of proteins.

Secretory vesicles

• Membrane-bound sacs from the Golgi, carrying proteins and lipids for release from the cell.

• Fuse with the plasma membrane and release contents out of the cell.

• Release of secretory vesicle contents may depend upon a signal to the cell.

Lysosomes and peroxisomes • Lysosomes are membrane-bound vesicles which contain

hydrolytic enzymes. Their function is to digest foreign substances and cell debris

• Peroxisomes are membrane-bound vesicles which contain enzymes which break down fatty acids, amino acids, and hydrogen peroxide.

Cytoskeletal Elements

• Microtubules (largest): made of tubulin; maintain cell shape, form the mitotic spindle during cell division, transport substances within the cell.

• Intermediate filaments: provide cell stability, anchor proteins to plasma membrane.

• Microfilaments (smallest): made of contractile proteins; involved in cell mobility, contraction.

Centrioles

Composed of microtubules. Direct the formation of the mitotic spindle during cell division; also contribute to the

structure of cilia and flagella.

Cell Division

Cell division: The mechanism by which one cell is duplicated to form two identical daughter cells. Involves separation of duplicated DNA(mitosis) and actual splitting of the cell (cytokinesis).

Interphase: 90% of cell cycle; normal function of cell. Just before entering mitosis, DNA is duplicated.

Mitosis: segregation of duplicated DNA

Four phases of mitosis: prophase, metaphase, anaphase, and telophase.

What happens during each phase? Prophase: DNA condensation into chromosomes, formation of

the mitotic spindle begins, breakdown of the nuclear membrane and nucleolus.

interphase

Centromere

Chromosome prophase

Mitosis

Metaphase: chromosomes migrate to middle of the cell, attach to the mitotic spindle. Form the metaphase plate.

Anaphase: centromeres of chromosomes split, chromosomes migrate away from each other

metaphase anaphase

telophase, cytokinesis

cleavage furrow

Mitosis and Cytokinesis

• Telophase: chromosomes decondense, nuclear membranes reform, spindle disappears.

Cytokinesis: Division of the cytoplasm, resulting in two daughter cells. Begins in anaphase, but not really part of mitosis.

Interphase Prophase Metaphase

Anaphase Telophase, cytokinesis Daughter cells

Microscopic appearance of mitotic phases

Next Lecture.....

Tissues