Question

#1 Describe the Na+/K+ pump

#2 sketch and describe how a cell would replicate a fragment of DNA whose leading strand has the sequence 5'CATGATTACATAC 3'

Answer 1

Answer 1. The sodium–potassium pump was discovered in 1957 by the Danish scientist Jens Christian Skou. Sodium potassium pump is an enzyme found in cell membrane. It is an active pump means for every ATP molecule that the pump uses, three sodium ions are exported and two potassium ions are imported, hence there is a net export of a single positive charge per pump cycle.

Function-

Resting potential-

To maintain cell membrane potential, cells keep a low concentration of sodium ions and high levels of potassium ions within the cell. The sodium–potassium pump mechanism moves 3 sodium ions out and moves 2 potassium ions in, thus, in total, removing one positive charge carrier from the intracellular space.

Control cell volume- It maintain cell volume with the help of osmolarity. Osmolarity of a cell is the sum of the concentrations of the various ion, proteins and other organic compounds inside the cell. When this is higher than the osmolarity outside of the cell, water flows into the cell through osmosis. This can cause the cell to swell up. The sodium potassium pump helps to maintain the right concentrations of ions.

Transport of molecule-

Active transport collectively called pumps or carrier proteins, work against electrochemical gradients. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive changes.

The primary active transport system uses ATP to move a substance, such as an ion, into the cell, and at the same time, a second substance is moved out of the cell. The sodium-potassium pump, spend energy to move potassium ions into the cell and a different number of sodium ions out of the cell. Concentration and charge difference across the membrane is just a result of this action pump.

Secondary active transport is the movement of material using the energy of the electrochemical gradient established by primary active transport. Using the energy of the electrochemical gradient created by the primary active transport system, other substances such as amino acids and glucose can be brought into the cell through membrane channels. These process is constitute of two phase.

Endocytosis-

Endocytosis is a type of active transport that moves large molecules into a cell. The plasma membrane of the cell invigilates, by forming a pocket around the target particle. The pocket pinches off, resulting in the particle being contained in a newly created vacuole that is formed from the plasma membrane. This is a process of Phagocytosis by which large particles, such as cells, are taken in by a cell. A variation of endocytosis is called pinocytosis this process takes in solutes that the cell needs from the extracellular fluid.

A targeted variation of endocytosis employs binding proteins in the plasma membrane that are specific for certain substances. The particles bind to the proteins and the plasma membrane invaginates, bringing the substance and the proteins into the cell. If passage across the membrane of the target of receptor-mediated endocytosis is ineffective, it will not be removed from the tissue fluids. Instead, it will stay in those fluids and increase in concentration.

Exocytosis-

In contrast to above method of moving material into a cell is the process of exocytosis. Exocytosis is the opposite of the processes discussed above in that its purpose is to expel material from the cell into the extracellular fluid. A particle enveloped in membrane fuses with the interior of the plasma membrane. This fusion opens the membranous envelope to the exterior of the cell, and the particle is expelled into the extracellular space.

Answer 2.

When replication begins, the two parent DNA strands are separated the DNA template is read in 3′ to 5′ direction whereas a new strand is synthesized in the 5′ to 3′ direction.

DNA is read by DNA polymerase in the 3′ to 5′ direction, meaning the nascent strand is synthesized in the 5' to 3' direction. And the leading strand is the strand of nascent DNA which is synthesized in the same direction as the growing replication fork. This sort of DNA replication is continuous.