Cell and Its Organelles
- Name the prominent cellular organelles and state their functions in cells.
- Explain the structure of the plasma membrane
What's inside a typical human cell?
Let's see each one in detail.
Characteristic features of a nucleus
- The nucleus is made up in large part of the chromosomes that carry a complete blueprint of all the individual characteristics of the animal. Each chromosome is made up of a giant molecule of DNA.
- The DNA strand is wrapped around a core of histone proteins to form a nucleosome. The whole complex of DNA and proteins is called chromatin.
- The nucleus of most cells contains a nucleolus, a patchwork of granules rich in RNA. They are the site of synthesis of ribosomes.
- The interior of the nucleus has a skeleton of fine filaments that are attached to the nuclear membrane or envelope, which surrounds the nucleus.
- The membrane is permeable only to small molecules. However, it contains nuclear pore complexes.
Over a billion years ago, aerobic bacteria were engulfed by eukaryotic cells and evolved into mitochondria, providing the eukayotic cells with the ability to form ATP by oxidative phosphorylation.
Characteristic features of mitochondria
- Each eukaryotic cell can have hundreds to thousands of mitochondria.
- In mammals, they are generally depicted as sausage-shaped organelles, but their shape can be quite dynamic.
- Each mitochondrion has an outer membrane, an intermembrane space, an inner membrane which is folded to form shelves (cristae), and a central matrix space.
- Mitochondria have their own genome, but with much less DNA than in the nuclear genome.
Did you know?
Mitochondria are exclusively maternal in origin, since the zygote mitochondria are derived from the ovum.
They are either smooth or rough!!!
Characteristic features of Golgi apparatus
- The Golgi apparatus is a collection of membrane-enclosed sacs (cisternae) that are stacked like dinner plates. One or more Golgi apparati are present in all eukaryotic cells, near the nucleus.
- The Golgi apparatus is a polarized structure, with cis and trans sides.
What is the mechanism of Golgi vesicular traffic?
Membranous vesicles containing newly synthesized proteins bud off from the rough endoplasmic reticulum and fuse with cistern on the cis side of the golgi apparatus.
The proteins are then passed via other vesicles to the middle cisterns and finally to the cistern on the trans side, from which vesicles branch off into the cytoplasm.
From the trans Golgi, vesicles shuttle to the lysosomes and to the cell exterior.
Watch the video that explains the golgi vesicular traffic.
- Lysosomes are large, irregular structures surrounded by membranes seen in the cytoplasm of a cell.
- Their interior is more acidic than the rest of the cytoplasm, which is maintained by the action of a proton pump.
- External materials such as endocytosed bacteria, worn-out cell components are digested inside the lysosomes, which contain over 40 types of hydrolytic enzymes.
Characteristic features of Peroxisomes
- Peroxisomes are 0.5 µm in diameter, are surrounded by a membrane, and contain enzymes that can either produce H2O2 (oxidases) or break it down (catalases).
- Peroxisomes can form by budding of the endoplasmic reticulum, or by division.
- The matrix of the peroxisomes contains more than 40 enzymes, which operate in concert with enzymes outside the peroxisome to catalyze a variety of anabolic and catabolic reactions (eg, breakdown of lipids).
- The ribosomes are complex structures, containing many different proteins and atleast 3 ribosomal RNAs.
- Each ribosome is made up of a large subunit and a small subunit called, on the basis of their rates of sedimentation in the ultracentrifuge, the 60S and 40S subunits.
- The ribosomes that get attached to the rough endoplasmic reticulum synthesize all transmembrane proteins, most secreted proteins, and most proteins that are stored in the Golgi apparatus, lysosomes and endosomes.
- The free ribosomes synthesize cytoplasmic proteins such as hemoglobin and the proteins found in peroxisomes and mitochondria.
Features of Centrosomes
- The centrosome, which is usually seen near the nucleus of a typical cell, is made up of two centrioles and surrounding amorphous pericentriolar material.
- The centrioles are short cylinders arranged so that they are at right angles to each other.
- Microtubules in groups of three run longitudinally in the walls of each centriole.
- The centrosomes are microtubule-organizing centers(MTOCs) that contain γ-tubulin.
- When a cell divides, the centrosomes duplicate themselves, and the pairs move apart to the poles of the mitotic spindle, where they monitor the steps in cell division.
The cell, with all the organelles listed above, is surrounded by a selectively permeable membrane called the plasma membrane
Integrate with Biochemistry to know the selectively permeable nature of the plasma membrane.
Let's learn about the plasma membrane in detail.
Characteristic features of plasma membrane
plasma membrane is generally is 7.5 nm (75 AO) thick.
major lipids present in the membrane are phospholipids such as phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine.
phospholipid molecules contain a head end and a tail end. The head end of
the molecule contains the phosphate portion and is relatively soluble in water
(polar, hydrophilic), and the tail ends are relatively insoluble (nonpolar, hydrophobic).
hydrophilic ends of the molecules are exposed to the aqueous environment that
bathes the exterior of the cells and the aqueous cytoplasm; the hydrophobic
ends meet in the water-poor interior of the membrane.
which makes up on average 50% of the mass of the membrane, exist as separate
globular units and many pass through or are embedded in one leaflet of the
membrane (integral proteins), whereas
others (peripheral proteins) are
associated with the inside or outside of the membrane.
in the membrane serve many functions. They act as cell adhesion molecules (anchor the cells to their neighbors or
basal lamina), as pumps (active
transport of ions across membrane), as carriers (facilitated diffusion), as ion channels (passage of ions into or out of the cell), as receptors (bind ligands or messenger molecules), and some act as enzymes (catalyze reactions at the
Yoshinori Ohsumi, a Japanese cell biologist, was awarded the Nobel Prize in Physiology or Medicine 2016, for his discoveries on how cells recycle their content, a process known as autophagy, a Greek term for "self-eating."
Lysosomes contain enzymes for digestion of cellular contents. A type of vesicle called autophagosome exists within the cell. As the autophagosome forms, it engulfs cellular contents, such as damaged proteins and organelles. Finally, it fuses with the lysosome, where the contents are degraded into smaller constituents.
Read more about the research through: Source link
|Mitochondrial||Briefing on the types, causes, symptoms and treatment of various mitochondrial diseases||Mitochondrial disease. Wikipedia, the free encyclopedia. 23 May 2017; accessed through the link on 25 May 2017. Source link|
|Lysosomal storage diseases||An extensive list on lysosomal storage diseases.||LIST OF LYSOSOMAL DISORDERS.LDNZ. accessed on 25 May 2017. Source link|
|The cytoskeleton||Description on the cytoskeleton of a cell||The Cytoskeleton - Kimball's Biology Pages.07 Dec 2013. accessed on 05 July 2017.
External link Source link
The video takes you on a quick tour inside the human cell and its organelles.
With the help of a diagram, write briefly about:
- Plasma membrane
- Endoplasmic reticulum
- Golgi apparatus