Eukaryotic Cells Have a Variety of Membranous Organelles Which Can Be Isolated for Study

Sugar Crush Detox

Natural Remedies for Food Cravings

Get Instant Access

Typical eukaryotic cells (Fig. 1-7) are much larger than prokaryotic cells—commonly 5 to 100 ^m in diameter, with cell volumes a thousand to a million times larger than those of bacteria. The distinguishing characteristics of eukaryotes are the nucleus and a variety of membrane-bounded organelles with specific functions: mitochondria, endoplasmic reticulum, Golgi complexes, and lysosomes. Plant cells also contain vacuoles and chloroplasts (Fig. 1-7). Also present in the cytoplasm of many cells are granules or droplets containing stored nutrients such as starch and fat.

In a major advance in biochemistry, Albert Claude, Christian de Duve, and George Palade developed methods for separating organelles from the cytosol and from each other—an essential step in isolating biomolecules and larger cell components and investigating their

(a) Animal cell

Ribosomes are protein-synthesizing machines

Peroxisome destroys peroxides

Cytoskeleton supports cell, aids in movement of organells

Lysosome degrades intracellular debris

Transport vesicle shuttles lipids and proteins between ER, Golgi, and plasma membrane

Golgi complex processes, packages, and targets proteins to other organelles or for export

Smooth endoplasmic reticulum (SER) is site of lipid synthesis and drug metabolism

Ribosomes are protein-synthesizing machines

Peroxisome destroys peroxides

Cytoskeleton supports cell, aids in movement of organells

Cytoskeleton

Nuclear envelope segregates chromatin (DNA + protein) from cytoplasm

Chloroplast harvests sunlight, produces ATP and carbohydrates

Starch granule temporarily stores carbohydrate products of photosynthesis

Starch Lipid Complex

Smooth endoplasmic reticulum (SER) is site of lipid synthesis and drug metabolism

Golgi complex

Thylakoids are site of light-driven ATP synthesis

Plasmodesma provides path between two plant cells

Cell wall of adjacent cell

Glyoxysome contains enzymes of the glyoxylate cycle

FIGURE 1-7 Eukaryotic cell structure. Schematic illustrations of the two major types of eukaryotic cell: (a) a representative animal cell and (b) a representative plant cell. Plant cells are usually 10 to 100 ^m in diameter—larger than animal cells, which typically range from 5 to 30 ^m. Structures labeled in red are unique to either animal or plant cells.

Nuclear envelope segregates chromatin (DNA + protein) from cytoplasm

Plasma membrane separates cell from environment, regulates movement of materials into and out of cell

Cytoskeleton

Chloroplast harvests sunlight, produces ATP and carbohydrates

Starch granule temporarily stores carbohydrate products of photosynthesis

Thylakoids are site of light-driven ATP synthesis

Cell wall provides shape and rigidity; protects cell from osmotic swelling

Golgi complex

Vacuole degrades and recycles macromolecules, stores metabolites

Plasmodesma provides path between two plant cells

Cell wall of adjacent cell

Glyoxysome contains enzymes of the glyoxylate cycle

FIGURE 1-7 Eukaryotic cell structure. Schematic illustrations of the two major types of eukaryotic cell: (a) a representative animal cell and (b) a representative plant cell. Plant cells are usually 10 to 100 ^m in diameter—larger than animal cells, which typically range from 5 to 30 ^m. Structures labeled in red are unique to either animal or plant cells.

(b) Plant cell structures and functions. In a typical cell fractionation (Fig. 1-8), cells or tissues in solution are disrupted by gentle homogenization. This treatment ruptures the plasma membrane but leaves most of the organelles intact. The homogenate is then centrifuged; organelles such as nuclei, mitochondria, and lysosomes differ in size and therefore sediment at different rates. They also differ in specific gravity, and they "float" at different levels in a density gradient.

(a) Differential centrifugation

Tissue homogenization

Tissue homogenization

Low-speed centrifugation (l,000 g, l0 min)

Tissue homogenate

Low-speed centrifugation (l,000 g, l0 min)

Tissue homogenate

Pellet contains whole cells, nuclei, cytoskeletons plasma membranes

Supernatant subjected to medium-speed centrifugation (20,000 g, 20 min)

Supernatant subjected to high-speed centrifugation (80,000 g, l h)

Pellet contains whole cells, nuclei, cytoskeletons plasma membranes

Pellet contains mitochondria, lysosomes, peroxisomes

Supernatant subjected to very high-speed centrifugation (150,000 g, 3 h)

Supernatant subjected to very high-speed centrifugation (150,000 g, 3 h)

Pellet contains microsomes (fragments of ER), small vesicles

Differential centrifugation results in a rough fraction-ation of the cytoplasmic contents, which may be further purified by isopycnic ("same density") centrifugation. In this procedure, organelles of different buoyant densities (the result of different ratios of lipid and protein in each type of organelle) are separated on a density gradient. By carefully removing material from each region of the gradient and observing it with a microscope, the biochemist can establish the sedimentation position of each organelle

Organelles Liver Cells

FIGURE 1-8 Subcellular fractionation of tissue. A tissue such as liver is first mechanically homogenized to break cells and disperse their contents in an aqueous buffer. The sucrose medium has an osmotic pressure similar to that in organelles, thus preventing diffusion of water into the organelles, which would swell and burst. (a) The large and small particles in the suspension can be separated by centrifugation at different speeds, or (b) particles of different density can be separated by isopycnic centrifugation. In isopycnic centrifugation, a centrifuge tube is filled with a solution, the density of which increases from top to bottom; a solute such as sucrose is dissolved at different concentrations to produce the density gradient. When a mixture of organelles is layered on top of the density gradient and the tube is centrifuged at high speed, individual organelles sediment until their buoyant density exactly matches that in the gradient. Each layer can be collected separately.

(b) Isopycnic

(sucrose-density) centrifugation

Pellet contains ribosomes, large macromolecules

Supernatant contains soluble proteins

Centrifugation

Centrifugation

Sample

Sucrose gradient

Less dense — component

More dense -component

Fractionation

Was this article helpful?

0 0
Low Carb Diets Explained

Low Carb Diets Explained

You can burn stored body fat for energy and shed excess weight by reducing the carbohydrate intake in your diet. Learn All About The Real Benefits of Low Carb Diets And Discover What They Can Really Do To Improve The Quality Of Your Life Today.

Get My Free Ebook


Responses

  • Vanessa Gibson
    Which cell organelle has maximum specific gravity?
    8 years ago
  • YVONNE
    Is an eukaryotic cell has a variety of membraneous organelle?
    8 years ago
  • Esa-Pekka
    How cytoskeleton aids in movement of organelle?
    8 years ago
  • kimberly
    Where is the lipid in the plant cell?
    8 years ago
  • giorgia
    Which organelle harvests and produces atp?
    8 years ago
  • Carol
    Does a eukaryotic cell have a variety of membranous organelles?
    8 years ago
  • FRANZISKA
    Does eukaryotic cells has a variety of membranous organelles?
    8 years ago
  • Ahmad
    Does a eukaryotic has variety of membranous organell?
    8 years ago
  • Lily
    Which organelle aids movement of the cell?
    8 years ago
  • roxy
    Where plant lipid store?
    8 years ago
  • Albert
    What produces atp in cell?
    8 years ago

Post a comment