The Nucleus, Nuclear Organisation and Karyotype

Question 1

Eukaryotic cells include…

Answer 1

…all plants and animals as well as many single celled organisms: algae, amoebae, fungi and moulds

Question 2

Eukaryotes are cells with …

Answer 2

…a true nucleus

Question 3

Unlike prokaryotes, eukaryotic cells contain …

Answer 3

…extensive internal membranes that define a collection of subcellular structures – organelles

Question 4

The cytoplasm also contains a network of fibres called the …

Answer 4

…cytoskeleton

Question 5

The cytoskeleton gives the cell…

Answer 5

…strength and rigidity and also control movement within the cell.

Question 6

Plant cells are surrounded by…

Answer 6

…a rigid cell wall and contain a large membrane bound vacuole and chloroplasts.

Question 7

Size of prokaryotes?

Answer 7

2mm (2 x 10-6 m)

Question 8

Size of eukaryotes?

Answer 8

10 – 100 mm
(1x10-5 – 1x10-4 m)

Question 9

Amount of DNA in prokaryotes?

Answer 9

1.36 mm

Question 10

Amount of DNA eukaryotes?

Answer 10

990 mm

Question 11

Number of genes in prokaryotes?

Answer 11

4377

Question 12

Number of genes in eukaryotes?

Answer 12

30-38000

Question 13

DNA organisation of prokaryotes?

Answer 13

1 circular chromosome in nucleoid

Question 14

DNA organisation of eukaryotes?

Answer 14

2 or more chromosomes in membrane bound nucleus

Question 15

Despite their differences, prokaryotic and eukaryotic cells have many …

Answer 15

…biochemical pathways in common – thus believed to have descended from the same ancestral cell.

Question 16

What is the nucleus surrounded by?

Answer 16

a double membrane

Question 17

What does the inner membrane of the nucleus do?

Answer 17

Defines the nucleus

Question 18

Describe the outer membrane of the nucleus.

Answer 18

continuous with rough endoplasmic reticulum (ER)

Question 19

Function of the nucleolus?

Answer 19

nuclear organizer, RNA / Ribosome synthesis occurs here.

Question 20

WHats chromatin?

Answer 20

combination of DNA and protein

Question 21

Whats nucleoplasm?

Answer 21

equivalent to the cytoplasm but in the nucleus – nucleotides and enzymes are dissolved in here.

Question 22

Function of nuclear pores?

Answer 22

serve as channels regulating the movement of material between the nucleus and the cytoplasm

Question 23

Give an example of something which leaves the nucleus via nuclear pores.

Answer 23

mRNA leaves the nucleus via a nuclear pore to be transcribed in the cytoplasm.

Question 24

What actually are nuclear pores?

Answer 24

protein complexes (~100 proteins) >1250 kDa, tightly regulate what goes in and out of nucleus.

Question 25

How many nuclear pores are there per nucleus?

Answer 25

There are around 3000 – 4000 pores per nucleus.

Question 26

In addition to mRNA, what else can move through nuclear pores?

Answer 26

proteins can also move through the nuclear pores. (Why would we need proteins to move into the nucleus?)

Question 27

Why would we need proteins to move into the nucleus?

Answer 27

- Gene expression - DNA replication and repair - RNA processing and transport

Question 28

How does RNA and Ribosome synthesis occur?

Answer 28

This occurs via transcription of the ribosomal RNA genes.

Question 29

In the nucleolus, a number of different sized...

Answer 29

...rRNA molecules are formed which, with proteins, make up the ribosome.

Question 30

How many strands of rRNA do eukaryotic ribosomes contain?

Answer 30

Eukaryotic ribosomes contain four strands of rRNA

Question 31

What are the four strands of rRNA in eukaryotic ribosomes?

Answer 31

28S, 18S, 5.8S, and the 5S rRNAs

Question 32

What does the S value indicate?

Answer 32

the “S” values indicate the size of the Strand “s” is the Svedberg coefficient

Question 33

What is the S value a measure of?

Answer 33

a measure of the rate of sedimentation under the influence of density gradient sedimentation.

Question 34

The genes for most of the rRNAs (28S, 18S, and 5.8S rRNAs), used to construct the ribosome are found...

Answer 34

...in the nucleolus

Question 35

Function of RNA polymerase I?

Answer 35

transcribes the 28S, 18S, and 5.8S rRNAs as a single unit within the nucleolus, which results in a 45S ribosomal precursor RNA.

Question 36

This 45S pre-rRNA synthesised by RNA polymerase I is processed to become...

Answer 36

...the 18S rRNA of the 40S (small) ribosomal subunit and to the 28S and 5.8S rRNAs of the 60S (large) ribosomal subunit.

Question 37

Function of RNA Polymerase III ?

Answer 37

transcribes the 5S rRNA, which is also found in the 60S ribosomal subunit; this process takes place outside of the nucleolus.

Question 38

The ribosomal subunits created are the ...

Answer 38

...60S and 40S subunits; these subunits join during protein synthesis to form the whole 80S ribosome.

Question 39

Human nuclear DNA is around ...

Answer 39

...2m in length

Question 40

To fit within a living cell ...

Answer 40

...DNA must be extensively compacted

Question 41

Compacting of DNA is aided by...

Answer 41

...DNA-binding proteins (such as histones)

Question 42

Length of DNA in a human cell =

Answer 42

2m

Question 43

Total length of DNA in human body =

Answer 43

74,400,000,000 km

Question 44

DNA is not ‘naked’ in the nucleus: exists as a...

Answer 44

nucleoprotein complex known as Chromatin (histone / DNA complex =nucleosome)

Question 45

What are the 5 different histone classes?

Answer 45

H1, H2a, H2b, H3 and H4 (in a nucleosome there is: 1H1, 2H2a, 2H2b, 2H3 and 2H4 = 9)

Question 46

What is Phosphorylation with kinase enzymes ?

Answer 46

kinase enzymes add phosphate groups

Question 47

Phosphorylation with kinase enzymes can promote...

Answer 47

...nucleosome loosening to allow DNA replication and transcription.

Question 48

Removal of phosphate groups from histones with phosphatase enzymes ...

Answer 48

...promotes DNA condensation (i.e. chromosome formation).

Question 49

What enzyme is used to remove phosphate groups from histones?

Answer 49

phosphatase enzymes

Question 50

Describe Chromosome territories

Answer 50

the different chromosomes will occupy different regions of the Nucleus.

Question 51

DNA exists in a complex with ...

Answer 51

...histone proteins inside the nucleus (chromatin)

Question 52

DNA wraps around a...

Answer 52

...histone protein core, forming structures known as nucleosomes

Question 53

Each nucleosome consists of ...

Answer 53

...8 histone proteins, with 146 base pairs of DNA wrapped around 1.67 times in a left-handed supercoil, giving a beads on a string appearance.

Question 54

Biochemical modification of the DNA and histone proteins allows for ...

Answer 54

...the opening (euchromatin) or condensing (heterochromatin) of the DNA.

Question 55

Heterochromatin and Euchromatin are important for...

Answer 55

...gene expression control as well as mitosis.

Question 56

Chromosomes can be stained and examined using...

Answer 56

...light microscope.

Question 57

Whats a karyotype?

Answer 57

Organising the chromosomes by size and shape.

Question 58

The chromosomes can be organised by size and shape into a ...

Answer 58

...karyotype

Question 59

In humans there are usually [...] of each chromosome (diploid 2C) in our [...] cells.

Answer 59

In humans there are usually *two* of each chromosome (diploid 2C) in our *somatic* cells.