Cell Fractionation

The cell homogenate contains large and small ^ organelles._

Cell Fractionation

The heaviest organelles can be removed and the remaining suspension re-centrifuged until the next heaviest organelles reach the bottom of the tube.

4.8 Cell Fractionation The organelles of cells can be separated from one another after cells are broken open and centrifuged.

Nuclei

Nuclei

The heaviest organelles can be removed and the remaining suspension re-centrifuged until the next heaviest organelles reach the bottom of the tube.

Lamina Nuclear

The nuclear lamina is a network of filaments just inside the nuclear envelope. It interacts with chromatin and helps support the envelope to which it is attached.

4.9 The Nucleus Is Enclosed by a Double Membrane The double-membraned nuclear envelope, nucleolus, nuclear lamina, and nuclear pores are common features of all cell nuclei. The pores are the gateways through which proteins from the cytoplasm enter the nucleus and genetic material (mRNA) from the nucleus enters the cytoplasm.

20 nm

An octagon of protein complexes surrounds each nuclear pore. Protein fibrils on the nuclear side form a cagelike structure.

The nuclear lamina is a network of filaments just inside the nuclear envelope. It interacts with chromatin and helps support the envelope to which it is attached.

4.9 The Nucleus Is Enclosed by a Double Membrane The double-membraned nuclear envelope, nucleolus, nuclear lamina, and nuclear pores are common features of all cell nuclei. The pores are the gateways through which proteins from the cytoplasm enter the nucleus and genetic material (mRNA) from the nucleus enters the cytoplasm.

20 nm

An octagon of protein complexes surrounds each nuclear pore. Protein fibrils on the nuclear side form a cagelike structure.

4.10 Chromatin and Chromosomes

(a) When a cell is not dividing, the nuclear DNA is aggregated with proteins to form chromatin, which is dispersed throughout the nucleus. (b) The chromatin in a dividing cell is packed into dense bodies called chromosomes.

Dense chromatin near the nuclear envelope is attached to the nuclear lamina.

Diffuse chromatin is in the nucleoplasm.

Dense chromatin near the nuclear envelope is attached to the nuclear lamina.

Diffuse chromatin is in the nucleoplasm.

Nucleoplasm And Cytoplasm

1 um

1 um

Ribosomes are the sites of protein synthesis

In prokaryotic cells, ribosomes float freely in the cytoplasm. In eukaryotic cells they occur in two places: in the cytoplasm, where they may be free or attached to the surface of the endoplasmic reticulum (described in the next section); and inside the mitochondria and chloroplasts, where energy is processed. In each of these locations, the ribosomes are the sites where proteins are synthesized under the direction of nucleic acids. Although they seem small in comparison to the cell in which they are contained, ribosomes are huge machines made up of several dozen kinds of molecules.

The ribosomes of prokaryotes and eukaryotes are similar in that both consist of two different-sized subunits. Eukary-otic ribosomes are somewhat larger, but the structure of prokaryotic ribosomes is better understood. Chemically, ribosomes consist of a special type of RNA, called ribosomal RNA (rRNA), to which more than 50 different protein molecules are noncovalently bound.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • Saimi Pohjonen
    Where would old cell organelles be broken?
    6 years ago
  • p
    How is a nuclear envelope similar to a cell membrane?
    1 year ago

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