Importance of Control Processes Essay

The cell cycle

- The cell cycle is a series of events that occur in order to produce two genetically identical daughter cells

- Tightly controlled by specific genes and highly regulated

- During interphase, the cell prepares to divide by replicating DNA and organelles

- Then the mitotic phase begins, starting with prophase, where the nuclear envelope breaks down and chromosomes condense. The centrioles move to opposite poles of the cell and the microtubules form a mitotic spindle

- Metaphase involves chromosomes lining up along the equator of the cell, attached to the spindle by the centromere

- When the chromosomes are aligned, anaphase begins where the chromosomes seperate into two chromatids at the centromere

- During telophase the spindle disappears and a new nuclear envelope forms around the chromosomes, the chromosomes decondense. The cytoplasm then splits and two daughter cells are formed

- This process is useful for growth of an organism or repairing damaged cells, however must be regulated

- Tumor supressor genes slow down the rate of cell division and repair mistakes in DNA by destroying cells with faulty DNA (apoptosis), maintaining the normal rate of cell division

- If a tumour surpressor gene becomes mutated it is switched off and no longer expressed, causing uncontrolled cell growth

- While most of the time these cells die, those that survive can continue dividing and form a tumor which may be malignant (cancerous)

- Therefore the role of tumor surpressor genes are important in controlling cell division as without them cells would divide uncontrollably and lead to health issues

Movement of substances across membranes

- Useful substances such as glucose and amino acids must be transported across the cell membrane so that they can be used in processes like respiration

- However, the cell membrane must also prevent unwanted substances from entering the cell, therefore it needs to be selectively permeable in order to control this

- Phospholipid membrane is arranged in a phospholipid bilayer, with hydrophilic fatty acid tails facing inside and hydrophobic phosphate heads facing outside

- This acts as a barrier to large or charged molecules, but allows smaller, uncharged molecules like oxygen and water to pass through

- If this bilayer wasn't present it would be difficult to control the passage of substances thus difficult to regulate metabolism

- Channel proteins within the cell membrane are selective in controlling the molecules they allow to cross

- e.g. aquaporins are channel proteins that allow water to rapidly pass through the cell membrane

Enzymes

- DNA replication is a process that relies heavily on the activity of enzymes such as DNA helicase and DNA polymerase

- Catalyse a wide range of metabolic processes within organisms

- Work by lowering the activation energy of a reaction, allowing it to occur at a lower temperature

- Have an active site complementary to the substrate so each enzyme is specific

- DNA helicase unravels the double helix structure whilst DNA polymerase joins the adjacent nucleotides together via a condensation reaction to produce the new DNA strand

- Enzymes can be affected by changes in pH, temperature, or the presence of inhibitors

- Enzymes in the body work at an optimum temperature of around 37 degrees

- Any lower than this and the reaction will be too slow, any higher than this and the enzymes will become denatured and their active site will change shape, rendering them unable to function

- When enzymes are denatured, it affects the function of many metabolic processes such as that of DNA replication

Aerobic Respiration

- The control of the movement of electrons is important in aerobic respiration during oxidative phosphorylation to produce ATP

- Electrons move down the electron transport chain and lose energy at each carrier

- This energy is used to pump H+ from the mitochondrial matrix into the intermembrane space where H+ concentration increases, creating an electrochemical gradient

- H+ diffuse down the electrochemical gradient into the matrix via the ATP synthase enzyme

- This leads to the formation of ATP from ADP and Pi

- The ATP can then be used for energy so that the organism can carry out other processes such as muscle contraction

- Therefore without the control of the movement of electrons, ATP would be unable to be synthesised as there would not be enough energy to form the electrochemical gradient

DNA Replication

- DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules

- The double helix structure is first unwound by breaking hydrogen bonds using DNA helicase

- Each original strand acts as a template

- Free DNA nucleotides air with their complementary bases on the original template strands

- DNA polymerase joins the nucleotides of the two strands together by a condensation reaction

- If DNA replication did not occur or was not controlled properly, the organism would be missing parts of its genome which would affect its function