Cell Biology MCQ - IIT JAM MCQ

Meiosis I is reduction in which separation of homologous chromosomes occur, while Meiosis II is equational division, just like mitosis in which separation of sister chromatids occur.
Eg.

In paracrine signaling, signaling cell and target cell both differ.

In the S-phase of the cell cycle, the amount of DNA doubles but the number of chromosomes remain same. So, DNA level here ranges from 3 picogram to 6 picogram, so amount is doubling.

Tubulin is the basic monomer of the microtubule.
Firstly, tubulin units are polymerised to give a protofilament and then proto filaments are arranged to form a microtubule.
So steps are
Nucleation → Polymerisation → Steady state
So in nucleation step gamma tubulins are required.

KDEL sequence is retention signal or retrieval sequence for ER-retention of the protein
K = Lysine
D = Aspartic acid
E = Glutamic acid
L = Leucine

Vinblastin is microtubule polymerisation inhibitor
Quabain is inhibitor of Na⁺ – K⁺ pump
Tunicamycin  blocks first step of N-linked glycosylation

The toxin from Clostridium botulinum inhibits the release of acetylcholine, the neurotransmitter at myoneural junctions. As a result, motor nerve impulses cannot be transmitted across the junction, and muscle cells are not stimulated to contract.

Mutations in the BRCA 1 gene, a breast tumor supressor gene, are the major cause of breast cancer. In most breast cancers involving this gene, deoxyribonucleic acid synthesis proceeds, indicating that the G1-S checkpoint is not affected; however, the mutated cells cannot control the transition between G2 and M. Moreover, the mutated cells have abnormal centrosome numbers, and their nuclear division does not proceed normally, leading to aneuploidy and genetic instability of the daughter cells.

The glycocalyx (cell coat) is associated with the outer leaflet of the plasma membrane. It is composed primarily of proteoglycans, which possess polysaccharide side chains. 

Smooth endoplasmic reticulum possesses mixed-function oxidases. Drugs detoxification occurs in hepatocytes following proliferation of the SER in response to the drug phenobarbital; the oxidases that metabolize this drug are located in the SER.

A microtubule consists of α - and β-tubulin dimers polymerized into a spiral around a hollow lumen to form a fairly rigid tubule. When cross-sectioned, the microtubule reveals 13 protofilament strands, which represent the tubulin dimers present in one complete turn of the spiral.

In the G-protein coupled receptor signaling if effector molecule is Adenylate cyclase then it forms cAMP from ATP. cAMP then activates protein-Kinase A.
If effector molecule will be

Non-polar amino acids are present in α -helix region of the integral proteins.

In the G₀ phase the cell is metabolically active
cdc-25 is a phosphatase and it is involved in the last step of formation of active MPF. For G₁ to S transition cyclin -E is required.

Ions move from high concentration to low concentration. Here the sodium concentration gradient is established. So Na⁺ movement occurs from outside to inside with transported proteins thats why facilitated diffusion.

Cancerous cells have the following properties
(i) Loss of contact inhibition
(ii) Growth factor independent
(iii) Autocrine growth stimulation
(iv) Less adhesive than normal cells (loss of E-Cadherin, the principal adhesion molecule of epithelical cells)
(v) Angiogenesis
(vi) Failure to undergo apoptosis
(vii) Expression of high level of telomerase
(viii) Immortal
(ix) Cell cycle check points abnormal 

In the S-phase of cell cycle, the amount of DNA doubles. So in S-phase, 8 picogram will double as 16 picogram. And then G2 phase will occur.

Meiosis-I is a reductional division, hence after meiosis-I, chromosome numbers are reduced to half. Here the reduced chromosomes are 14 and meiosis-II is an equational division, so 14 chromosomes will be there after meiosis-II.