Lecture 6

Question 1

All cells, with a few exceptions, have nuclei. What are the exceptions?

Answer 1

• Mammalian red blood cells

- Platelets

Question 2

What do eukaryotic cells store in the nucleus?

Answer 2

Where eukaryotic cells store their genetic information (DNA)

Question 3

What is the nucleus composed of?

Answer 3

• Nuclear envelope
• Chromatin
• Nucleolus
• Nuclear Pores
• Nucleoplasm

Question 4

How many nucleus are there per cell?

Answer 4

One

Question 5

What is the nuclear envelope?

Answer 5

• A double-layered membrane (lipid bilayer) in which the nucleus is enclosed
• Isolates nuclear material from the cytoplasm
• Only allows for the transfer of small molecules in and out of the nucleus

Question 6

What is found between the two membranes of the nuclear envelope?

Answer 6

Perinuclear space

Question 7

Where are the inner and outer membrane of the nuclear envelope joined?

Answer 7

At the nuclear pore

Question 8

What does the outer layer of the nuclear envelope consist of?

Answer 8

Ribosomes

Question 9

Nuclear lamina?

Answer 9

• Found adjacent to the inner face of the nuclear envelope
• Consists of a fine network of
  protein filaments…(Intermediate filaments)
• Provides structural support to the nuclear envelope
• Aids in the positioning of the nuclear pores

Question 10

Nuclear pore function?

Answer 10

- Allows the transport of water-soluble
molecules across the nuclear envelope and
into the nucleus.
– Molecules which can pass though include:
• RNA
• Ribosomes
• Proteins
• Carbohydrates
• Signal molecules
• Lipids

Question 11

Nuclear pore structure?

Answer 11

• Ring-like arrangement called
  a pore complex
• Cytoplasmic face which has 8 subunits that surround a central zone, which contains a channel, connecting to the nuclear face

Question 12

What is the nucleoplasm?

Answer 12

• Maintains the structure and shape of the nucleus
• The cytoplasm in the nucleus
• Highly viscous liquid that surrounds the chromosomes and nucleoli
• Many substances such as nucleotides and enzymes are dissolved in the nucleoplasm

Question 13

Nucleoside?

Answer 13

Purine or Pyrimidine base linked to either a ribose or
deoxyribose sugar (no phosphate group)

Question 14

Nucleotide?

Answer 14

A series of nucleosides joined together by a phosphate
group by ester linkage to the sugar. DNA and RNA are polymers of
nucleotides

Question 15

Nuclear matrix?

Answer 15

• A network of fibres, which can also be found in the nucleoplasm
• Similar to cell cytoskeleton
• Precise composition and
  arrangement in the nucleus not
  known

Question 16

What is the primary protein component of

chromatin?

Answer 16

Histones. Tightly pack DNA, in order for it to fit in a cell.

Question 17

What is the process of chromatin packing?

Answer 17

• The histones organise the DNA in nucleosomes
• The nucleosome is further folded to form chromatin fibres
• Chromatin fibres further condense into chromosomes

Question 18

What is chromatin mainly formed of?

Answer 18

• DNA
• RNA
• Proteins (Histones)

Question 19

What are the two different types of chromatin?

Answer 19

Euchromatin and Heterochromatin

Question 20

Euchromatin?

Answer 20

–Lightly packed form of chromatin

–DNA is transcribed from Euchromatin

Question 21

Heterochromatin?

Answer 21

–Tightly packed form of DNA
–Usually located at the periphery of the
nucleus
–The DNA in heterochromatin is not transcribed
–The functions of heterochromatin are attributed to the dense packing of the DNA:
•Gene regulation
•Protection of the integrity of chromosomes

Question 22

What is one nucleosome?

Answer 22

147 DNA base pairs

wrapped around a set of 8 histones

Question 23

Diploid?

Answer 23

• Cell or organism that has paired or two sets of chromosomes, one of each parent
• In sexually reproducing species, the number of chromosomes in the cells in the body (somatic) is
  diploid
• Double the number of chromosomes as haploid

Question 24

Haploid?

Answer 24

• Cell or organism that has just a single copy of each chromosome
• Haploid number are found in gametes or sex cells
• Half the number of chromosomes as diploid

Question 25

Human karyotype?

Answer 25

23 pairs of chromosomes:

• 22 pairs of autosomes
• 1 pair of allosomes (sex chromosomes)

Question 26

Nucleolus function?

Answer 26

• Associated with specific regions of several chromosomes which
  transcribe ribosomal RNA (rRNA)
  • rRNA found in other cytoplasmic organelles called ribosomes
  • Ribosomes are closely connected with protein synthesis
  • Ribosomes contain roughly equal amounts of RNA and proteins
• Within the nucleolus chromosomal DNA transcribes rRNA which then
  associates with proteins to form ribosomal particles

Question 27

Nucleolus structure?

Answer 27

• Dense basophilic (you can see it under a microscope) material in
  nucleoplasm
• Disappear during cell division
• Re-appear post-division (Re-appearance organized by particular chromosomes which have an area called nucleolar organiser region)

Question 28

Nucleolar organiser region?

Answer 28

Chromosomal regions crucial for the formation of the nucleolus

Question 29

Ribosomal RNA?

Answer 29

Non-coding (nothing gets transcribed from them, so no proteins are made)

Question 30

Nucleoli contain chromosomal regions that specialise in making what?

Answer 30

RNA

Question 31

Does transcription takes place in the cytoplasm of a cell?

Answer 31

No, it takes place in the nucleus

Question 32

A single cell in a smoker’s lung has become cancerous. It doubles its DNA and divides much faster than a normal lung cell. The most likely change that would have caused this condition took place in which region of the cell?

Answer 32

The nucleus