Lecture 10: Nucleus

Question 1

The Nucleus

Answer 1

The most prominent organelle (5-10 µm diameter)

One nucleus per cell (in most cases)

Contains most of the cell’s genes

Serves as repository of inherited genetic information

Some additional genes are found in the mitochondria
and chloroplasts

The cell’s control centre

Question 2

What is the nucleus surrounded by?

Answer 2

Nuclear Envelope

Question 3

What is the nuclear envelope made up of?

Answer 3

Which is
composed of two
membranes

Each membrane is
a phospholipid
bilayer

Question 4

Nuclear Pore Complex

Answer 4

Controls the movement of
molecules out of, or into the
nucleus

OUT: mRNA, tRNA and
ribosomal subunits

mRNA (messenger RNA)
carries information from a
gene

tRNA (transfer RNA) and
ribosomal subunits are
needed to build proteins

Question 5

Nuclear Pore Complex

Answer 5

Controls the movement of
molecules out of, or into the
nucleus

IN: control signals, building
materials and energy
- when to turn a gene on or off
- the building “blocks” for RNA
- energy for chemical
synthesis

Question 6

What is inside the nucleus?

Answer 6

Inner surface of
nuclear envelope is
lined by the nuclear
lamina

Question 7

What is the nuclear lamina made up of?

Answer 7

Which is composed of
intermediate filaments

Maintain shape of
nucleus

Helps organise the
packing of the DNA
within the nucleus

Question 8

The nucleolus

Answer 8

A prominent nuclear structure within non-dividing cells

May be two or more
nucleoli per cell
depending on species
and stage of cell cycle.

The nucleolus is
responsible for making
ribosomal RNA which
combines with proteins to
produce ribosomes

Question 9

What is a nucleotide polymer?

Answer 9

DNA

Question 10

What are the proteins that the helix interacts with called?

Answer 10

The helix interacts with specific

proteins called histones (H2-H4)

Question 11

DNA organisation within the nucleus

Answer 11

Further interactions between
the DNA and another histone
(H1) cause the 10nm fibre to
coil to form the 30nm fibre

This 30nm fibre then loops to
form 300nm fibre

During cell division the 300nm
fibres coil to form metaphase
chromosomes

Question 12

During cell division the 300nm fibres coil to form?

Answer 12

Metaphase chromosomes

Question 13

what can metaphase chromosomes be displayed as?

Answer 13

Karyotype - which can be used to screen for chromosomal defects

Question 14

Euchromatin in nucleus

Answer 14

less dense contains genes being used by that cell

Question 15

Heterochromatin

Answer 15

More dense contains genes not being used by that cell

dynamic relationship between euchromatin and heterochromatin

Question 16

What is the nuclear envelope made of?

Answer 16

the nuclear membranes, nuclear pore complexes, and nuclear lamina