The Nucleus, Nuclear Organisation and Karyotype Flashcards
Eukaryotic cells include…
…all plants and animals as well as many single celled organisms: algae, amoebae, fungi and moulds
Eukaryotes are cells with …
…a true nucleus
Unlike prokaryotes, eukaryotic cells contain …
…extensive internal membranes that define a collection of subcellular structures – organelles
The cytoplasm also contains a network of fibres called the …
…cytoskeleton
The cytoskeleton gives the cell…
…strength and rigidity and also control movement within the cell.
Plant cells are surrounded by…
…a rigid cell wall and contain a large membrane bound vacuole and chloroplasts.
Size of prokaryotes?
2mm (2 x 10-6 m)
Size of eukaryotes?
10 – 100 mm
(1x10-5 – 1x10-4 m)
Amount of DNA in prokaryotes?
1.36 mm
Amount of DNA eukaryotes?
990 mm
Number of genes in prokaryotes?
4377
Number of genes in eukaryotes?
30-38000
DNA organisation of prokaryotes?
1 circular chromosome in nucleoid
DNA organisation of eukaryotes?
2 or more chromosomes in membrane bound nucleus
Despite their differences, prokaryotic and eukaryotic cells have many …
…biochemical pathways in common – thus believed to have descended from the same ancestral cell.
What is the nucleus surrounded by?
a double membrane
What does the inner membrane of the nucleus do?
Defines the nucleus
Describe the outer membrane of the nucleus.
continuous with rough endoplasmic reticulum (ER)
Function of the nucleolus?
nuclear organizer, RNA / Ribosome synthesis occurs here.
WHats chromatin?
combination of DNA and protein
Whats nucleoplasm?
equivalent to the cytoplasm but in the nucleus – nucleotides and enzymes are dissolved in here.
Function of nuclear pores?
serve as channels regulating the movement of material between the nucleus and the cytoplasm
Give an example of something which leaves the nucleus via nuclear pores.
mRNA leaves the nucleus via a nuclear pore to be transcribed in the cytoplasm.
What actually are nuclear pores?
protein complexes (~100 proteins) >1250 kDa, tightly regulate what goes in and out of nucleus.
How many nuclear pores are there per nucleus?
There are around 3000 – 4000 pores per nucleus.
In addition to mRNA, what else can move through nuclear pores?
proteins can also move through the nuclear pores. (Why would we need proteins to move into the nucleus?)
Why would we need proteins to move into the nucleus?
- Gene expression
- DNA replication and repair
- RNA processing and transport
How does RNA and Ribosome synthesis occur?
This occurs via transcription of the ribosomal RNA genes.
In the nucleolus, a number of different sized…
…rRNA molecules are formed which, with proteins, make up the ribosome.
How many strands of rRNA do eukaryotic ribosomes contain?
Eukaryotic ribosomes contain four strands of rRNA
What are the four strands of rRNA in eukaryotic ribosomes?
28S, 18S, 5.8S, and the 5S rRNAs
What does the S value indicate?
the “S” values indicate the size of the Strand “s” is the Svedberg coefficient
What is the S value a measure of?
a measure of the rate of sedimentation
under the influence of density gradient sedimentation.
The genes for most of the rRNAs (28S, 18S, and 5.8S rRNAs), used to construct the ribosome are found…
…in the nucleolus
Function of RNA polymerase I?
transcribes the 28S, 18S, and 5.8S rRNAs as a single unit within the nucleolus, which results in a 45S ribosomal precursor RNA.
This 45S pre-rRNA synthesised by RNA polymerase I is processed to become…
…the 18S rRNA of the 40S (small) ribosomal subunit and to the 28S and 5.8S rRNAs of the 60S (large) ribosomal subunit.
Function of RNA Polymerase III ?
transcribes the 5S rRNA, which is also found in the 60S ribosomal subunit;
this process takes place outside of the nucleolus.
The ribosomal subunits created are the …
…60S and 40S subunits; these subunits join during protein synthesis to form the whole 80S ribosome.
Human nuclear DNA is around …
…2m in length
To fit within a living cell …
…DNA must be extensively compacted
Compacting of DNA is aided by…
…DNA-binding proteins (such as histones)
Length of DNA in a human cell =
2m
Total length of DNA in human body =
74,400,000,000 km
DNA is not ‘naked’ in the nucleus: exists as a…
nucleoprotein complex known as
Chromatin (histone / DNA complex =nucleosome)
What are the 5 different histone classes?
H1, H2a, H2b, H3 and H4 (in a nucleosome there is: 1H1, 2H2a, 2H2b, 2H3 and 2H4 = 9)
What is Phosphorylation with kinase enzymes ?
kinase enzymes add phosphate groups
Phosphorylation with kinase enzymes can promote…
…nucleosome loosening to allow DNA replication and transcription.
Removal of phosphate groups from histones with phosphatase enzymes …
…promotes DNA condensation (i.e. chromosome formation).
What enzyme is used to remove phosphate groups from histones?
phosphatase enzymes
Describe Chromosome territories
the different chromosomes will occupy different regions of the Nucleus.
DNA exists in a complex with …
…histone proteins inside the nucleus (chromatin)
DNA wraps around a…
…histone protein core, forming structures known as nucleosomes
Each nucleosome consists of …
…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.
Biochemical modification of the DNA and histone proteins allows for …
…the opening (euchromatin) or condensing (heterochromatin) of the DNA.
Heterochromatin and Euchromatin are important for…
…gene expression control as well as mitosis.
Chromosomes can be stained and examined using…
…light microscope.
Whats a karyotype?
Organising the chromosomes by size and shape.
The chromosomes can be organised by size and shape into a …
…karyotype
In humans there are usually […] of each chromosome (diploid 2C) in our […] cells.
In humans there are usually two of each chromosome (diploid 2C) in our somatic cells.
