Question

essay question: 1.explain why all cells must have the four parts all cells have.

2. Be able to compare and contrast prokaryotic and eukaryotic cellular characteristics. (including DNA location, cell wall makeup)

Answer 1

Q1) Cell is the basic structural,functional and biological unit of a living organism. British scientist Robert Hooke first discovered it in 1665. Cells give structure to the body, take nutrients from food, convert the nutrients into energy, and carry out specialized functions. They also contain the body’s hereditary material by which they are able to make copies of themselves .

A cell basically consists of four parts i) Plasma membrane or cell membrane ii) cytoplasm iii) Ribosome iv) DNA .These four parts of cell are important for the functionality of a cell.

Role of these parts are i) plasma membrane or cell membrane - It is the outermost layer of cell, made up of lipo-protein bilayer, it is the boundary or barrier between the cell and its environment, it gives cell a shape, regulates the entry and exit of substances into and out of the cell. It acts like a guard of cell giving permission what to enter and what not .

Plasma membrane is made up of a phospholipid bilayer, having two layers of phospholipids back-to-back. Phospholipids are the lipids with a phosphate group attached to them. They have one head and two tails. The head is polar and hydrophilic, or water-loving. The tails are nonpolar and hydrophobic, or water fearing. As water is the main component of living organisms, both inside and outside the cell, the phospholipids remain in two layers, with heads pointing outward and the tails in the middle. The plasma membrane also contains two types of proteins, they are i) peripheral proteins and ii) integral proteins. These proteins act like channels to allow the molecules to enter and leavethe cell.

ii) Cytoplasm is present within the cell membrane in all cell types and it contains all organelles and cell parts. It is made up of a watery substance,called cytosol, it contains various cell structures like mitochondria, ribosome, lysosome etc.Many important processes occurs in cytoplasm.

iii) Ribosome -

The Ribosome is a complex molecule made of ribosomal RNA molecules and proteins, helps in protein synthesis found in cytoplasm.It is associated with the endoplasmic reticulum membrane. Each ribosome has a large part and a small part , together they form a single unit made up of several ribosomal RNA molecules and many proteins. The ribosome is responsible for translating encoded messages from messenger RNA molecules to synthesize proteins from amino acids. The ribosome translates each codon, or the set of three nucleotides, of the mRNA template and matches it with the appropriate amino acid by the translation process. The amino acid is provided by a transfer RNA (tRNA) molecule. Each newly translated amino acid gets added to the growing protein chain till ribosome completes the process of protein synthesis. Protein is an important building block of bones, muscles, cartilage, skin, and blood,  they make enzymes, hormones, and other body chemicals required for body's various processes.

iv) DNA- DNA contains the cell's hereditary information and controls the cell's growth and reproduction. It is the command center of a cell, It also contains genetic informations required to make proteins,

So all the four structures are necessery for the existance of a cell , plasma membrane gives a form to a cell , cytoplasm maintains the cell structure , ribosome creates the building blocks of cell that is proteins required for various processes to maintain a cell, DNA is required for reproduction and for instruction of various processes of a cell.

Q2) The basic difference between eukaryotes and prokaryotes are, eukaryotic cells contain membrane-bound organelles,like nucleus, but prokaryotic cells do not have this . They also differ in various cellular structures.

Prokaryotes- These  are the organisms without a cell nucleus, or any other membrane-bound organelles. Most of them are usually unicellular, but few prokaryotes like myxobacteria are multicellular.

Eukaryotes - These are the organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. They have membrane bound nucleus. Examples are Animals, plants, fungi, and protists.

Difference between Eukaryote and prokaryote:-

The basic difference between an eukaryotes and prokaryote is euukaryotes have a "true" nuclei having their DNA, but in prokaryotes the genetic material is not membrane-bound.

In eukaryotes, the mitochondria and chloroplasts does various metabolic processes but in prokaryotes similar processes occur across the cell membrane.

The cell walls of prokaryotes contains  peptidoglycan or murein, it is specific feature of prokaryotes, it gives the cell shape and surrounds the cytoplasmic membrane. Peptidoglycan is a huge polymer of disaccharides (glycan) cross-linked by short chains of identical amino acids (peptides) monomers. The backbone of the peptidoglycan molecule is made up of two derivatives of glucose: N-acetylglucosamine (NAG) and N-acetlymuramic acid (NAM). The NAG and NAM strands are synthesized in the cytosol of the bacteria. They are connected by inter-peptide bridges.

In eukaryotes animal cells do not have cell wall , but plant cells have cell wall and are made up of cellulose.

Prokaryotes contain only a single loop of stable chromosomal DNA stored in an area called nucleoid, but in eukaryote DNA is found on tightly bound and organised chromosomes.Some eukaryotes have satellite DNA structures called plasmids, but plasmid is the charatceristic feature of prokaryotes, many important genes in prokaryotes are stored on plasmids.

In eukaryotes lysosome and peroxisomes are present but absenyt in prokaryotes.

Microtubules and ER are present in eukaryotes but absent in prokaryotes.

Mitochondria are present in eukaryotes but absent in prokaryotes.

Ribosome are larger in eukaryotes but smaller in prokaryotes.

Golgi-apparatus is present in eukaryotes but absent in prokaryotes.

Prokaryotes have a larger surface area to volume ratio, so there metabolic rate is high,as a result they have a higher growth rate leading to a shorter generation time when compared to Eukaryotes.