Lecture 11: How Are Cellular Events Controlled? Flashcards
What is the most prominent organelle and how big is it?
The nucleus, 5-10μm in diameter.
Does the nucleus hold all of the cell’s genes?
Most, but not all.
What is the function of the nucleus?
Serves as repository of genetic information and the cell’s control centre.
What surrounds the nucleus?
The nuclear envelope.
Describe the nuclear envelope. (2)
Composed of two membranes, each a phospholipid bilayer. Inner surface is lined by the nuclear lamina.
What is the nuclear lamina made of?
Intermediate filaments.
What is the function of the nuclear lamina?
• helps maintain shape
of nucleus
• and organise the
packing of the DNA
What happens if nuclear lamina is defective?
Hutchinson-Gilford Progeria syndrome
cell nuclei have abnormal shape, results in accelerated aging
What is the purpose of nuclear pores? (3)
- mRNA, rRNA and tRNA out of nucleus
- control signals move into nucleus
- energy and materials into nucleus
What type of polymer is DNA?
A nucleotide polymer.
How much DNA does each human cell contain?
about 2.5m (250,000x diameter of nucleus)
DNA must be very well _____ but also _________.
DNA must be very well PACKED but also ACCESSIBLE.
How are chromatin fibres formed?
DNA double helix combined with histone proteins.
Chromatin fibres undergo _____-______ _______
Chromatin fibres undergo multi-level packaging
What is the diameter of a DNA double helix?
About 2nm
What is the diameter of a chromatin
About 10nm
What is a nucleosome?
A length of DNA coiled around a core of histones (a bead) (multiple nucleosomes form a chromatin).
How does a 10nm chromatin fibre form a 300nm fibre?
Chromatin fibres further interact with another histone (H1) and cause to 10nm fibre to coil and form a 30nm fibre. The 30nm fibre loops to form a 300nm fibre.
What happens to the 300nm fibres during metaphase?
During cell division the 300nm fibres coil to
form metaphase chromosomes.
What is euchromatin?
A less dense, genetically active (often) region of chromatin during interphase.
What is heterochromatin?
A dense, genetically inactive region of chromatin during interphase.
Is the location of a chromosome within a nucleus random?
No.
