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Cell Structure Part 2

Nucleus:
A central part of cell which regulates the cellular activities and responsible for reproduction is called as nucleus. Depending on the number of nucleus present in a cell, it is divided into different types –
  • Uninucleate – one nucleus is present
  • Binucleate – Two nucleuses is present
  • Human RBC and sieve tubes lack nucleus.

Nucleus contains nuclear membrane, nucleolus, nucleoplasm and chromatin.

Nuclear membrane:
  • Double layered tubular structure
  • Nuclear pores occurs at various places which allows transform of material from inside the nucleus to its outside cytoplasm
  • Outer layer is attached with endoplasmic reticulum

Nucleolus:
  • Round in shape and without membrane
  • Synthesize Ribosomal RNA

Nucleoplasm:
  • Fluid portion within the nucleus

Chromatin:
  • Entangled mass of thread like structure
  • Contains DNA, RNA and proteins
  • During the process of cell division, chromatin material gets organized into chromosomes
  • Chromosomes contain information for inheritance of features from parents to offsprings in the form of DNA.
  • DNA contains genes which are responsible for hereditary characters and contain the information necessary for constructing and organizing cells.
  • Proteins are of histone and non histone kinds
  • Chromosomes occur in pairs, one from the maternal side and other from the paternal side. Their number is diploid (2n) in somatic cells and haploid (n) in gametes.
  • DNA and histone proteins are equal in amount in chromosome whereas the amount of RNA and non histone proteins are variable and low in amount.

Cell Organelles:
Every cell needs a lot of chemical activities to support their complicated structure and function. To keep these activities of different kinds separate from each other, cells use membrane bound little structures called as organelles within themselves.

Cell organelles include endoplasmic reticulum, Golgi bodies, lysosomes, mitochondria, plastids and vacuoles. They are very much important to carry out crucial functions in the cells.


Endoplasmic reticulum (ER):

Definition: A large network of tubular shapes spread throughout the cytoplasmic region is called endoplasmic reticulum and it forms a skeletal structure in cytoplasm.

Types of ER:
1.  Smooth ER
·  Do not possess of lipids

2.  Rough ER
·  Contains ribosome on the outer surface
·  Helps in protein synthesis


Function of ER:
  • Synthesis various proteins like serum protein, peripheral proteins, lysosomes etc
  • Synthesize fat molecules or lipids
  • Act as a channel for the transport of materials between various regions of cytoplasm and the nucleus
  • Helps in biochemical activities done by cell
  • Plays a crucial role in detoxifying many poisons and drugs
  • Synthesize cholesterol and steroid hormones and transport them.

Golgi bodies:

Definition:
A membrane bound, bag like vesicles arranged in stacks near to ER is called Golgi bodies or Golgi apparatus. The material synthesized within the ER is packed and transported to various parts inside and outside the cell through the Golgi apparatus.


Function:
Synthesize glycoprotein and glycolipids
Helps in formation of lysosomes and secretes enzymes found in lysosomes
Helps in storage, modification and packaging of products in vesicles.



Self study:

Example-1: Match the following
(A) (B)
Nucleus DNA, RNA and Proteins
Nucleoplasm Synthesize Ribosomal RNA
Chromatin Central regulatory part of cell
Nucleolus Fluid portion within the nucleus

Answer:
(A) (B)
Nucleus Central regulatory part of cell
Nucleoplasm Fluid portion within the nucleus
Chromatin DNA, RNA and Proteins
Nucleolus Synthesize Ribosomal RNA

Example-2:  Outer layer of nuclear membrane is attached with ………….
a)  Plasma membrane
b)  Nucleus
c) 
Endoplasmic Reticulum
d)  Chromatin

Answer: Outer layer of nuclear membrane is attached with Endoplasmic Reticulum


Example-3: Glycoprotein and glycolipids are synthesized in ………………………
a)  Nucleus
b) 
Golgi apparatus
c)  Endoplasmic reticulum
d)  Chromatin

Answer: Glycoprotein and glycolipids are synthesized in Golgi apparatus.


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