Subject: Botany
Course Code: BOTDSC-151T
Program: FYUG (Four Year Undergraduate Programme)
Instructions: Answer any ten from Section-A and any five from Section-B. Figures in the margin indicate full marks.
The cell was discovered by Robert Hooke in the year 1665. He observed thin slices of cork under a primitive microscope and described the box-like structures as "cells".
Prions are infectious agents composed entirely of a protein material that can fold in multiple, abstract ways. Unlike viruses or bacteria, they contain no nucleic acids (DNA or RNA).
Example: Bovine Spongiform Encephalopathy (Mad Cow Disease) or Creutzfeldt-Jakob Disease (CJD) in humans.
| Feature | Archaebacteria | Eubacteria |
|---|---|---|
| Cell Wall | Lacks peptidoglycan | Contains peptidoglycan |
| Habitat | Extreme environments | Ubiquitous (everywhere) |
Smooth Endoplasmic Reticulum (SER) lacks ribosomes on its surface and is primarily involved in lipid synthesis and detoxification. Rough Endoplasmic Reticulum (RER) has ribosomes attached to its surface, giving it a "rough" appearance, and is the site for protein synthesis.
F1 particles (or elementary particles) are head-like structures found on the inner mitochondrial membrane attached to the F0 base. Function: They act as the ATP synthase enzyme complex, responsible for the synthesis of ATP during oxidative phosphorylation.
The 'S' stands for Svedberg unit, a measure of the sedimentation rate in an ultracentrifuge. Function: Ribosomes are the "protein factories" of the cell, translating genetic code into polypeptide chains.
tRNA (transfer RNA) is a small RNA molecule (70-90 nucleotides) with a cloverleaf secondary structure. Function: It acts as an adapter molecule that carries specific amino acids to the ribosome during translation based on the mRNA codon sequence.
Programmed cell death (PCD) is a genetically regulated process where a cell "commits suicide" in a controlled manner to maintain organismal health or development. Apoptosis is the most common form of PCD.
A proto-oncogene is a normal gene that helps cells grow. An oncogene is a mutated or high-expression version of a proto-oncogene that can cause a cell to become cancerous.
The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids. Function: It serves as the attachment site for spindle fibers (via the kinetochore) during cell division.
Rf Value = (Distance traveled by the substance) / (Distance traveled by the solvent front)
It is a dimensionless ratio used in chromatography to identify components in a mixture.
The stationary phase is the substance that stays fixed inside the chromatography column or on the plate. The mobile phase is the solvent (liquid or gas) that moves through the stationary phase, carrying the sample components with it.
Resolution is the ability of a microscope to distinguish two closely spaced objects as separate entities. It determines the level of detail visible in an image.
Prokaryotic cells are primitive cells lacking a defined nucleus, whereas eukaryotic cells are advanced cells with membrane-bound organelles.
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Nucleus | Absent (Nucleoid) | Present with nuclear membrane |
| Organelles | Membrane-bound organelles absent | Mitochondria, Golgi, ER present |
| Ribosomes | 70S type | 80S type (70S in organelles) |
| DNA | Circular, naked | Linear, associated with histones |
Mycoplasma: They are the smallest independent living organisms, characterized by the absence of a cell wall, making them pleomorphic and resistant to antibiotics like penicillin.
Structure:
Diseases: In humans, Mycoplasma pneumoniae causes atypical pneumonia. In plants, they cause diseases like 'Little leaf of Brinjal' and 'Witch's broom'.
Chemical Composition:
Fluid Mosaic Model: Proposed by Singer and Nicolson (1972).
The membrane is a "mosaic" of proteins embedded in or attached to a fluid lipid bilayer.
Function of Ion Channels: They are pore-forming proteins that allow the selective, rapid flow of specific ions (like Na+, K+, Ca2+) across the membrane down their electrochemical gradient, essential for nerve impulse conduction and muscle contraction.
(a) Ribosome: Composed of rRNA and proteins. Consists of two subunits (large and small). Function: Translation of mRNA into proteins.
(b) Mitochondria: Double-membrane structure. Inner membrane is folded into Cristae. The matrix contains DNA and enzymes. Function: Known as the "Powerhouse of the cell," it generates ATP through aerobic respiration.
Chemical Composition of DNA: DNA is a polymer of deoxyribonucleotides. Each unit consists of: 1. Deoxyribose sugar, 2. Phosphate group, 3. Nitrogenous bases (Adenine, Guanine, Cytosine, Thymine).
Nucleoside vs Nucleotide:
Types of RNA:
DNA Replication: The biological process of producing two identical replicas of DNA from one original DNA molecule.
Enzymes Required: Helicase (unwinding), Primase (RNA primer), DNA Polymerase III (elongation), DNA Polymerase I (primer removal), Ligase (joining fragments), Topoisomerase (tension relief).
Prokaryotic Process: Starts at a single origin (OriC). It involves initiation (formation of replication bubble), elongation (leading and lagging strands with Okazaki fragments), and termination.
(a) Cell Senescence: The phenomenon by which normal diploid cells lose the ability to divide, usually after about 50 doublings (Hayflick limit). It is a protective mechanism against cancer.
(b) Apoptosis: A form of programmed cell death characterized by cell shrinkage, chromatin condensation, and DNA fragmentation. It is essential for removing damaged or unnecessary cells without causing inflammation.
Cell Cycle: The series of events that take place in a cell leading to its division. Checkpoints (G1/S, G2/M) ensure the cell is ready to proceed to the next phase.
Events: Interphase (G1, S, G2) and M-phase (Mitosis/Cytokinesis). DNA replication occurs in the S-phase.
Function of CDK: Cyclin-Dependent Kinases (CDKs) are enzymes that, when bound to Cyclin proteins, trigger the transition between cell cycle phases by phosphorylating target proteins.
SEM (Scanning Electron Microscope) scans the surface of a specimen for 3D images. TEM (Transmission Electron Microscope) passes electrons through thin slices for internal 2D details.
SEM Principle: An electron beam scans the surface. Secondary electrons are emitted from the surface, detected, and converted into a 3D-like image on a monitor.
Applications: 1. Surface topography of cells. 2. Material science. 3. Forensic investigations.
HPLC (High-Performance Liquid Chromatography): A technique used to separate, identify, and quantify components in a mixture based on their interactions with a stationary phase under high pressure.
Functioning: A liquid mobile phase is pumped at high pressure through a column packed with stationary phase material. Components separate based on their affinity for the phases and are detected at the exit.
Applications: 1. Purifying proteins/nucleic acids. 2. Drug testing. 3. Monitoring environmental pollutants.