Cell Biology Test - 10

Chloroplasts contain grana, which are minute particles consisting of a pile of thin double platelets, containing chlorophylls and carotenoids associated with photosynthesis.

Extranuclear, or cytoplasmic, DNA, are located in two types of organelles found in the cytoplasm of the cell. These organelles are the mitochondria in animal and plant cells and the chloroplasts in plant cells. Chloroplast DNA (cpDNA) contains genes that are involved with aspects of photosynthesis and with components of the special protein-synthesizing apparatus that is active within the organelle.

Chromosomes are of following types on the basis of position of centromeres on them.
(i) Metacentric: Centromeres occur at the centre, thus such type of chromosomes contain two equal arms. At anaphase stage of cell division, these chromosomes are 'V' shaped.
(ii) Submetacentric: Centromeres are sub-median. They are 'L' shaped during anaphase.
(iii) Acrocentric: Centromeres are sub-terminal. They are 'J' shaped during anaphase.
(iv) Telocentric: Terminal centromeres are 'I' shaped during anaphase.
(v) Acentric: Chromosomes do not have centromeres. They are of rare occurrence.

Fluid mosaic model was proposed by Singer and Nicolson.
The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates.

The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids (a dyad). During mitosis, spindle fibers attach to the centromere via the kinetochore. The arms of chromosomes can be connected together with the help of centromere, in either metacentric, submetacentric, acrocentric or telocentric manner.

Chloroplast and mitochondria are called semi-autonomous organelles because they have their own genetic material (DNA) and are capable of synthesizing proteins required for their functioning.

Cristae are the folded structures that are formed by the in-foldings of inner mitochondrial membrane.

A cell can survive independently but not its organelles.

The control of nuclei over the phenotypic expression of the cell was studied in Acetabularia.
Acetabularia is a genus of single-celled green algae (family Polyphysaceae) found in subtropical seas. The algae are among the largest single-celled organisms and also feature an unusually large nucleus. Because part of one species can be grafted onto another, Acetabularia has been used to study the relative role of nucleus and cytoplasm in the genetic control of growth and development.

Nucleotides of DNA were first discovered by Oswarld Avery. Nucleotides in DNA contain four different nitrogenous bases: Thymine, Cytosine, Adenine, or Guanine. There are two groups of bases:
Pyrimidines: Cytosine and Thymine each have a single six-member ring.
Purines: Guanine and Adenine each have a double ring made up of a five-atom ring attached by one side to a six-atom ring.

The nucleus of cell was discovered by Robert Brown and the cell was discovered by Robert Hooke.The structure of cell membrane was first studied by Nageli and Cramer.Holler and his co-workers first studied the tRNA.