Cell Ultrastructure

Magnification → increases the size of an object

Resolution/resolving power → ability to distinguish between adjacent points

Table 1-10-2: Microscopes (1)

Feature 

Optical microscope

Electron microscope

Radiation

Light

Electrons

Magnification

400x (max1500)

≈500 000x

Resolution

2µm

1nm / 0,001µm

Electrons have a small wavelength

\ Higher resolution

Vacuum in microscope

Absent

Present

Specimen is

- Alive or dead

- Stained

- Dead (vacuum!)

Transmission microscope:

Electrons pass through internal

structure of specimen

Scanning microscope:

Beams of electrons are reflected

off specimens surface. Allows a

three dimensional view

Cell wall (plant cells only)

Made up of cellulose fibres which provide strength

Cell does not burst if surrounding solutions become dilute

Nucleus (5µm)

Contains chromosomes (genes made of DNA which control cell activities)

Separated from the cytoplasm by a nuclear envelope

The envelope is made of a double membrane containing small holes

These small holes are called nuclear pores (100nm)

Nuclear pores allow the transport of proteins into the nucleus

Rough Endoplasmic Reticulum (rough ER)

Have ribosomes attached to the cytosolic side of their membrane

Found in cells that are making proteins for export (enzymes, hormones, structural proteins, antibodies)

Thus, involved in protein synthesis

Modifies proteins by the addition of carbohydrates, removal of signal sequences

Phospholipid synthesis and assembly of polypeptides

Smooth Endoplasmic Reticulum (smooth ER)

Have no ribosomes attached and often appear more tubular than the rough ER

Necessary for steroid synthesis, metabolism and detoxification, lipid synthesis

Numerous in the liver

Ribosomes (20-30nm)

Small organelles often attached to the ER but also found in the cytoplasm

Large (protein) and small (rRNA) subunits form the functional ribosome

Subunits bind with mRNA in the cytoplasm

This starts translation of mRNA for protein synthesis (assembly of amino acids into proteins)

Free ribosomes make proteins used in the cytoplasm. Responsible for proteins that

go into solution in cytoplasm or

form important cytoplasmic, structural elements

Ribosomal ribonucleic acid (rRNA) are made in nucleus of cell

Golgi apparatus

Stack of flattened sacs surrounded by membrane

Receives protein-filled vesicles from the rough ER (fuse with Golgi membrane)

Uses enzymes to modify these proteins (e.g. add a sugar chain, making glycoprotein)

Adds directions for destination of protein package - vesicles that leave Golgi apparatus move to different locations in cell or proceed to plasma membrane for secretion

Involved in processing, packaging, and secretion

Other vesicles that leave Golgi apparatus are lysosomes

Vacuole and vesicles

Membranous sacs of liquid which store substances - vacuoles are storage areas

Lysosomes (0.05 to 0.5 micron)

Performs intracellular digestion - more numerous in cells performing phagocytosis

Limiting membrane keeps digestive enzymes separate from the cytoplasm

Lysosomal enzymes digest particles

They function optimally at pH 5 and are mostly inactive at cytosolic pH

Lysosomal enzymes are synthesized on rough ER

Transferred to the Golgi apparatus for modification and packaging

Primary lysosomes are small concentrated sacs of enzymes (no digestion process)

Primary lysosomes fuse with a phagocytic vacuole

Become secondary lysosomes

Digestion begins

Nutrients diffuse through lysosomal membrane into the cytosol

Mitochondria (1µm in diameter and 7µm in length)

Mostly protein, but also contains some lipid, DNA and RNA

Power house of the cell

Energy is stored in high energy phosphate bonds of ATP

Mitochondria convert energy from the breakdown of glucose into adenosine triphosphate (ATP)

Responsible for aerobic respiration

Metabolic activity of a cell is related to the number of cristae (larger surface area) and mitochondria

Cells with a high metabolic activity (e.g. heart muscle) have many well developed mitochondria

Chloroplast (4-6µm in diameter and 1-5µm in length)

Only in photosynthesising cells (plants)

Light energy, CO2, and H2O are converted to produce carbohydrates and O2

Inner membrane has folds, called lamellae (where chlorophyll is found), which surround a fluid, called stroma

Cells & Molecules

Cell Division

Cell Types

Cell Ultrastructure

Enzymes

Gene Technology

Genes, DNA, RNA

Large Molecules

Plasma Membrane

Respiration

Content

Cell Ultrastructure

Cell wall (plant cells only)

Nucleus (5µm)

Rough Endoplasmic Reticulum (rough ER)

Smooth Endoplasmic Reticulum (smooth ER)

Ribosomes (20-30nm)

Golgi apparatus

Vacuole and vesicles

Lysosomes (0.05 to 0.5 micron)

Mitochondria (1µm in diameter and 7µm in length)

Chloroplast (4-6µm in diameter and 1-5µm in length)