SSC CGL Biology · Cell Biology
Cell Division and Respiration
The enzymes that copy DNA, the first stage of meiosis and the word chromatin, and where each step of respiration happens and which step makes the most ATP.
Why this matters
Six questions in the bank, two from each year's shifts. Each asks one step and its place or its enzyme, so the two short tables here are enough.
Concept 1 of 2: DNA copying and cell division
Definition
DNA replication:
- Helicase opens the double helix.
- Primase lays down the RNA primer.
- DNA polymerase adds nucleotides.
- DNA ligase joins the fragments (it seals the 3' end of one piece to the 5' end of the next).
Division:
- Walther Flemming named chromatin in 1879 and coined mitosis in 1882.
- Prophase I of meiosis: leptotene (chromosomes begin to condense), then zygotene (homologues pair, synapsis), then pachytene (synapsis complete), diplotene, diakinesis.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 1 · Cell Biology · Cell Division and Respiration
| Column-A (Enzyme/Protein) | Column-B (Role in DNA replication) |
|---|---|
| i. Helicase | a. Joins the end of the new DNA fragment to the end of the previous one |
| ii. RNA primase | b. Nucleotide polymerisation |
| iii. DNA polymerase | c. RNA primer synthesis |
| iv. DNA ligase | d. Opens up the DNA double helix |
Leptotene is only the start
Concept 2 of 2: Respiration and ATP
Definition
The steps:
- Glycolysis, in the cytoplasm: glucose to pyruvic acid; a net 2 ATP.
- Krebs cycle, in the mitochondrial matrix: about 2 ATP.
- Electron transport chain, on the inner mitochondrial membrane: about 32 to 34 ATP, the most. Oxygen is the final electron acceptor and becomes water.
Without oxygen, yeast ferments sugar and gets only the 2 ATP of glycolysis. Glucose is the usual substrate for respiration.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 2 · Cell Biology · Cell Division and Respiration
Glycolysis is outside the mitochondria
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Respiration and ATP3 rows
Watch out for (2)
- Leptotene is only the start→ DNA copying and cell division
- Glycolysis is outside the mitochondria→ Respiration and ATP
Test yourself on Cell Biology
15 past SSC CGL questions from this chapter, timed at 9 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.