Chromosomes, the cell cycle and mitosis
Watch the whole lecture free
Make a free account to watch every lecture to the end: 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
That was the teaching part. The rest of this lecture is free with an account: 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
No password needed now: we email you a link to set one. Already have an account? Sign in, then come back to this page.
The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Copy, then split
- Chromosome structure
Read the transcript of the teaching part
Last time
Before we start: last time, in Membrane structure, diffusion and osmosis, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Copy, then split
Your body makes millions of new cells every minute. Each new cell needs exactly the same D N A as the cell it came from. So a cell first copies all its D N A, then shares it out equally. The copying and sharing follow a strict cycle, and this lesson walks through it.
Chromosome structure
A human cell has about two metres of D N A, squeezed into a nucleus a few micrometres across. The D N A is wound round histone proteins to make it compact. When a cell is about to divide, the D N A is copied. Each chromosome then consists of two identical sister chromatids joined at the centromere. The tips of each chromatid are the telomeres. They protect the ends of the D N A from damage and from joining to other chromosomes. Humans have forty-six chromosomes, in twenty-three pairs. After replication there are still forty-six chromosomes, but ninety-two chromatids.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Stages of mitosis.
The whole chapter: The Mitotic Cell Cycle, The Mitotic Cell Cycle.
Chapter 5: The mitotic cell cycle
- Chromosomes, the cell cycle and mitosis 6 min
- Stem cells, telomeres and cancer 5 min
Also for A Level Biology 9700
Which topics come up most in A Level Biology 9700 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency, Paper 4 topic frequency.