Nucleus

Question 1

what are ribosomes

Answer 1

complexes made of ribosomal RNA’s and proteins

Question 2

2 types of ribosomes

Answer 2

1. bound ribosomes: attached to rER
2. free ribosomes: in the cytoplasm

Question 3

2 functions of ribosomes

Answer 3

1. carry out translation
2. the more protein synthesis a cell needs to do, the more ribosomes it has

Question 4

what is the nucleus

Answer 4

is the most prominent organelle (5-10 micrometer) in the cell that contains most of the cell genetic information

Question 5

4 structural components of nucleus

Answer 5

1. nuclear envelope
2. nuclear proteins
3. tightly packed DNA
4. nucleolus (prominent area)

Question 6

what is the nuclear envelope

Answer 6

the 2 membranes, with perinuclear space in between, each made up of a phospholipid bilayer. the outer membrane continuous with ER

Question 7

what is the nuclear lamina

Answer 7

lines the inner membrane of the nuclear envelope and is composed of intermediate filaments (Lamin proteins)

Question 8

2 functions of nuclear lamina

Answer 8

1. maintains the shape of the nucleus
2. helps organize the packaging of the DNA within the nucleus

Question 9

what are the nuclear pores

Answer 9

channels made of proteins (nucleoporins) that form the nuclear pore complex

Question 10

the function of nuclear pores

Answer 10

controls the movement of molecules out of or into the nucleus (nucleo-cytoplasmic exchange)

Question 11

what is the nucleolus

Answer 11

is the prominent feature in non dividing cells that is a non membrane bound specialised region within the nucleus (may be multiple)

Question 12

function of the nucleolus

Answer 12

responsible for making ribosomal RNA and ribosomal subunits which is then transported out of nucleus and assembles as ribosomes in cytoplasm

Question 13

how is DNA organised within the nucleus

Answer 13

• DNA is a 2.5 nucleotide polymer
• double helix is about 2 nm in diameter
• helix interacts with histones (proteins H2-H4) which form a 10 nm diameter fiber
• further interactions between other histones (H1) causes fiber to coil and form the 30 nm fiber
• fibre then loops to form 300 nm fibre
• during cell division the 300 nm fibre coils to form metaphase chromosomes

Question 14

what is euchromatin

Answer 14

less electron-opaque, contains genes being used by that cell (unpacked genes)

Question 15

what is heterochromatin

Answer 15

more electron-opaque, contains genes not being used by that cell (packed genes)