Lecture 6 Flashcards
All cells, with a few exceptions, have nuclei. What are the exceptions?
- Mammalian red blood cells
- Platelets
What do eukaryotic cells store in the nucleus?
Where eukaryotic cells store their genetic information (DNA)
What is the nucleus composed of?
- Nuclear envelope
- Chromatin
- Nucleolus
- Nuclear Pores
- Nucleoplasm
How many nucleus are there per cell?
One
What is the nuclear envelope?
- 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
What is found between the two membranes of the nuclear envelope?
Perinuclear space
Where are the inner and outer membrane of the nuclear envelope joined?
At the nuclear pore
What does the outer layer of the nuclear envelope consist of?
Ribosomes
Nuclear lamina?
- 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
Nuclear pore function?
- 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
Nuclear pore structure?
- 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
What is the nucleoplasm?
- 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
Nucleoside?
Purine or Pyrimidine base linked to either a ribose or deoxyribose sugar (no phosphate group)
Nucleotide?
A series of nucleosides joined together by a phosphate
group by ester linkage to the sugar. DNA and RNA are polymers of
nucleotides
Nuclear matrix?
- 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
What is the primary protein component of
chromatin?
Histones. Tightly pack DNA, in order for it to fit in a cell.
What is the process of chromatin packing?
- The histones organise the DNA in nucleosomes
- The nucleosome is further folded to form chromatin fibres
- Chromatin fibres further condense into chromosomes
What is chromatin mainly formed of?
- DNA
- RNA
- Proteins (Histones)
What are the two different types of chromatin?
Euchromatin and Heterochromatin
Euchromatin?
–Lightly packed form of chromatin
–DNA is transcribed from Euchromatin
Heterochromatin?
–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
What is one nucleosome?
147 DNA base pairs
wrapped around a set of 8 histones
Diploid?
- 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
Haploid?
- 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
Human karyotype?
23 pairs of chromosomes:
- 22 pairs of autosomes
- 1 pair of allosomes (sex chromosomes)
Nucleolus function?
- 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
Nucleolus structure?
- 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)
Nucleolar organiser region?
Chromosomal regions crucial for the formation of the nucleolus
Ribosomal RNA?
Non-coding (nothing gets transcribed from them, so no proteins are made)
Nucleoli contain chromosomal regions that specialise in making what?
RNA
Does transcription takes place in the cytoplasm of a cell?
No, it takes place in the nucleus
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?
The nucleus
