The Nucleus Flashcards

1
Q

Key Concepts

A

The nucleus is a highly-specialized organelle committed primarily to
protecting, copying, and transcribing DNA (making an RNA copy).
The interior of the nucleus is highly compartmentalized.
Most cells contain a single nucleus – exceptions include muscle and
blood cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Nucleus

A

 Double membrane bound organelle
 Contains the hereditary information (DNA
genome)
 Site of DNA replication (DNA to DNA)
 Site of gene transcription (DNA to RNA)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Chromatin

A

DNA and associated
proteins within nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Nuclear envelope

A

double
membrane with nuclear pores

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Nucleolus

A

where rRNA and
proteins are assembled to form
ribosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Nucleoplasm:

A

remaining nuclear
content, similar to cytoplasm.
The nucleus contains several features that
distinguish it from other cellular structures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Envelope

A

 Double membrane.
 Separates genome from the
cytoplasm.
 Functionally, separates
transcription (RNA synthesis) in
the nucleus from translation
(polypeptide synthesis) in the
cytoplasm.
 Thousands of nuclear pores
perforate the nuclear envelope:
 Each measuring 9nm
 Regulate traffic between the two
compartments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Transcription

A

DNA mRNA  Protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

mRNA, tRNA and rRNA

A
  • Ribosomes consists of a few
    ribosomal RNA (rRNA) molecules
    and a variable number
    of ribosomal proteins.
  • Amino acids are incorporated into
    the growing polypeptide on the
    ribosome according to the
    sequence of codons of a mRNA.
  • tRNA carries appropriate amino
    acid to match code.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Chromatid

A

one-half of
two identical copies
of a replicated
chromosome.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Telomeres

A

caps
on chromosomes that
offer protection
during cell division

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q
A
  • Each chromosome
    contains DNA bound to
    histones
  • This packaging controls
    information available
  • DNA wrapped round
    histone = nucleosome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Visibility of chromosomes through
cell cycle

A

Immunofluorescence images:
green dye labels microtubules
and blue dye labels DNA.
* Centrosomes form before cell
division.
* Chromosomes become visible.
* Daughter cells have DNA in the
form of chromatin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

The code for life

A
  • DNA strands held together by hydrogen
    bonds between complementary bases:
    Adenine (A), Thymine (T), Cytosine (C) and
    Guianine (G)
  • Triple code system, where 3 bases is an
    intstruction for one amino acid.
  • The genetic code is the recipe for amino
    acids.
  • Proteins are made of amino acids.
  • The code is hidden until required. How?
    By wrapping around histones.
  • Enzymes such as Helicase and
    Topoisomerase work to uncoil DNA during
    replication or transcription
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

(Short tandem repeats –
STR)

A

Not all DNA codes for proteins
* ”Useless” codes that never translate are repeated
over and over again
* Number of “useless” code and repetition pattern
unique to each individual.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Euchromatin

A

loose
chromatin structure and active
for transcription

17
Q

Heterochromatin

A

condensed chromatin structure
and is inactive for transcription
Heterochromatin appears as dark patches in the nucleus
during interphase (i.e. non-dividing cells).

18
Q

DNA replication factories

A

form large
complexes in the nucleus devoted to
copying DNA with 100% accuracy
consist of DNA associated
with replication machineries, i.e.,
large protein complexes involved in
DNA replication

19
Q

Replisome:

A

smallest functional
unit in the factories, responsible for
copying one segment of DNA

20
Q

Nucleolus

A

 The nucleolus
contains DNA that
encodes ribosomal
RNAs (rRNA)
Nucleoli is the plural
of nucleolus
 Nucleoli are sites of
high transcriptional
activity for rRNA genes

21
Q

Functions of Nucleolus

A

 Not a membrane bound structure.
 Transcription of ribosomal RNA from DNA
 Packaging of rRNA with proteins to form
ribosomal sub-units:
 Proteins translated in the cytoplasm &
transported back to the nucleus

22
Q

The nuclear lamina

A

Beneath the inner
membrane, lies the
nuclear lamina.
* A meshwork of
intermediate filament
proteins called Lamins
and associated proteins

23
Q

Lamin Proteins

A

form
structures known as intermediate filaments
 Three types of lamin proteins: A-type, B-type
and C-type lamins
 Bind to the inner nuclear membrane giving
nuclear stability, organise chromosomes and
bind nuclear pore complexes
 Lamin proteins interact with chromosomes and
DNA, regulating gene expression

24
Q

The nuclear lamina structure

A
  • Nuclear Lamina fibres lie between nuclear pore complexes (NPC).
  • Lamins are anchored in place by membrane components
  • Several inner nuclear membrane proteins – interacts with DNA or DNA
    associated proteins
    helps control the shape of
    chromosomes and regulate heterochromatin and
    euchromatin
25
A multitude of proteins are needed in the nucleus
* Proteins involved in: * DNA replication * Transcription * RNA processing (splicing of exons) * Chromosome packaging (histones) * Ribosome construction (in the nucleolus) * Nuclear lamina * Envelope proteins * Protein trafficking through nuclear pore complexes
26
NPCs
 Nuclear pore complexes: Layers of rings stacked on top of one another that span the nuclear membranes, linked to filamentous protein fibrils to form a basket structure  Structure undergoes complex conformational changes when it transports material into and out of the nucleus
27
Nuclear Localisation Signals (NLS)
 Short peptide sequence acts like a postcode to direct the polypeptide to the nucleus  Composed of positively charged amino acids, e.g. Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val  Can be at the N-terminal of the polypeptide chain or internal  This signal sequence binds to a docking protein on the outer membrane of the nucleus, e.g. importin
28
Import / Export through nuclear pores
 Regulated by two carrier proteins:  Importin and Exportin  Importins and exportins are members of a family of nuclear transport receptors known as karyopherins
29
nuclear import/export system regulates traffic through nuclear pores
 Proteins transported in/out of nucleus in folded, functional state  Nuclear localization sequences (NLS) and nuclear export signals (NES) are amino acid sequences recognized by NLS and NES receptors  Direction of nuclear transport is controlled by a protein called Ran  Ran binds the nucleotide GTP (G-protein)  Ran acts like a waterwheel, moving in and out of the nucleus in a cycle powered by GTP.
30
When NLS met importin
Nuclear localisation signals (NLS) in a protein to be carried into the nucleus (the cargo) bind to nuclear transport receptors called importins The cargo/importin complex binds to proteins in the cytoplasmic filaments in the nuclear pore complex and is transported through the nuclear pore complex
31
journey via the Nuclear Pore
 The complex translocate to the nucleus via the NPC.  In the nucleus, Ran-GTP displaces the cargo protein, which is released
32
Importin-Ran-GTP then via the NP
The importin/Ran-GTP complex is then exported through the nuclear pore. GTPase-activating protein (Ran GAP) in the cytoplasm hydrolyses the GTP on Ran to GDP, releasing importin in cytoplasm.
33
Ran-GDP together with NTF2 return to the nucleus
The Ran/GDP is then transported back to the nucleus by binding to its own import receptor (NTF2).  In the nucleus, a guanine exchange protein (Ran GEF) reforms Ran-GTP.  Ran-GTP levels high in nucleus to support protein cargo-importin disruption. (part 2)
34
NPC Export
Proteins targeted for export from the nucleus have a sequence of amino acids called a nuclear export signal  Exportin proteins bind to these peptides and transport the protein back to the cytoplasm  Exportins also bind to Ran/GTP, but this time enable export of the cargo protein Nuclear export 2. Nuclear pore complex: Export  Following transport to the cytoplasm the GTP is hydrolysed to GDP and Ran/GDP is released from the cargo.  Exportins recycled back to the nucleus through the nuclear pore
35
Key Concepts
Because DNA stores all of the information necessary to survive, cells protect it from damage. This is especially evident in eukaryotic cells, which typically have much larger DNA molecules than prokaryotes. – In eukaryotes, the primary function of the nucleus is to sequester DNA in its own chemically-specialized compartment. Passage of large molecules (e.g., proteins) into and out of the nucleus is carefully regulated by a structure called the nuclear pore complex. The nucleus carefully protects a eukaryotic cell’s DNA * Key Concepts (2): – A secondary function of the nucleus is to physically shield the DNA from damage. Nuclear lamins are cytoskeletal proteins that form a tough, fibrous network attached to the inner surface of the nuclear membrane. This network protects DNA from mechanical force.