1. PHR 202
Biochemistry and Molecular Biology
Chapter 3:
Nuclear Structure and Function
Course instructor
Nashrah Mustafa
B.Pharm. (BRACU), MS in Biotechnology (BRACU), MSc Disease Mechanisms and
Therapeutics (Brunel University London)
Lecturer
School of Pharmacy
BRAC University
3. Chapter Contents
• Insight of cell types according to Nuclear
arrangement.
• Chromosomal structure and function. Disease
associated with Chromosomal defects.
• Cell cycle.
• Cell division: Mitosis and Meiosis.
4. Nucleus
• Nucleus is the control centre of a cell containing the genetic
material in an organism.
• It is only present in eukaryotes.
5. Nuclear Envelope
• Outer layer (ribosomes & rough ER are attached)
• Inner layer (Covered with nuclear lamina)
• Lamina are network of filaments which provided structural
• support to the envelope
• Chromatin remains attached to the nuclear lamina
• Nuclear pore (controls transportation between cell & nucleus)
Nucleolus
• rRNA synthesis
• Important for ribosome production
Chromatin
• DNA + Histone proteins
• Euchromatin (Loosely packed)
• Allows DNA replication, gene expression
• Heterochromatin (Tightly packed)
• Gene silencing
Nucleus
DNA replication and transcription process occur inside the nucleus
https://youtu.be/prYd9nE0Rks
6. There are variations in the way eukaryotes and prokaryotes hold
their genetic material inside the cell…….
Eukaryote vs Prokaryote: Genetic Material
7. Eukaryote vs Prokaryote: Genetic
Material
While eukaryotic cells have many linear DNA molecules called
chromosome, prokaryotes often have just one circular DNA
molecule/chromosome,
Eukaryotic chromosome
Nucleosome
8. Chromatin
• The DNA is packaged by special proteins termed histones. The formed protein/DNA
complex is called chromatin.
• The genes present in chromatin can either be turned off or on. It means in some cells a
certain part of the gene is active (“switched on”) while the other is not (“switched off”).
• What is regulating this complex information from genes to proteins and mRNA?
the chromatin
What are histones?
Histones are positively-charged basic proteins that bind to negatively-charged
phosphate molecules of DNA..
There are two major elements in a chromatin. They are the cell’s DNA and the associated
proteins. The associated proteins are known as histones. Or we can say that chromatin
contains proteins called histones
A nucleosome consists of a segment of DNA wound in sequence around eight histone
protein cores. The basic structural unit of chromatin is the nucleosome
https://youtu.be/gbSIBhFwQ4s
9. DNA and Chromosomes
A chromosome is an organized structure of DNA found in cells. It is
a single piece of coiled DNA containing many genes, regulatory
elements and other nucleotide sequences.
10. • The DNA is packaged by histones that
provides structural support for a
chromosome. The DNA wraps around
complexes of histone proteins, giving the
chromosome a more compact shape.
Histones also play a role in the
regulation of gene expression.
• A nucleosome consists of a segment of
DNA wound in sequence around eight
histone protein cores. In forming a
chromosome, the nucleosomes
repeatedly fold in on themselves to
tighten and condense the packaged
DNA (about six feet of DNA).
• The formed protein/DNA complex
is called chromatin. The basic
structural unit of chromatin is the
nucleosome.
14. Functions of a Chromosome
1. To control all the activities of a living cell.
2. Chromosomes contain genes, the unit of heredity. They control the
characteristic traits that are passed on from parents to offspring.
3. DNA and proteins are synthesized correctly because of
chromosomes, which are necessary for building muscles and tissues,
growth and repair, as well as for the synthesis of thousands of
enzymes.
4. Chromosomes are often referred to as the 'packaging material' that
hold DNA and proteins together in eukaryotic cells.
5. During cell division stages, it is the chromosome that is responsible
for the replication and distribution of DNA amongst new cells.
15. Chromosomes
• Chromosomes are threadlike structures made of protein and a single molecule of
DNA that serve to carry the genomic information from cell to cell.
• In plants and animals (including humans), chromosomes reside in the nucleus of
cells. Humans have 22 pairs of numbered chromosomes (autosomes) and one pair
of sex chromosomes (XX or XY), for a total of 46.
• Each pair contains two chromosomes, one coming from each parent, which means
that children inherit half of their chromosomes from their mother and half from their
father. Chromosomes can be seen through a microscope when the nucleus dissolves
during cell division.
• Chromosomes vary in number and shape among living organisms. Most bacteria
have one or two circular chromosomes (humans have linear chromosomes).
16. Chromosomes
• Each species of plants and animals has a set number of chromosomes (a fruit fly
has 4 pairs while a rice plant has 12).
• In humans, the twenty-third pair is the sex chromosomes. Typically, biologically
female individuals have two X chromosomes (XX) while those who are biologically
male have one X and one Y chromosome (XY). However, there are exceptions to
these rules.
• Chromosomes are also different sizes. The human X chromosome is about three
times larger than the human Y chromosome, containing about 900 genes, while the
Y chromosome has about 55 genes.
17. Chromosomes: Structure
• Following replication, the DNA condenses
into chromosomes. At this point, each
chromosome actually consists of a set of
duplicate chromatids that are held
together by the centromere. During the
intermediate stage in cell division, the
centromere duplicates, and the chromatid
pair separates; each chromatid becomes a
separate chromosome at this point.
• A telomere is a region of repetitive DNA
sequences at the end of a chromosome.
Telomeres protect the ends of
chromosomes from becoming tangled.
Each time a cell divides, the telomeres
become slightly shorter. Eventually, they
become so short that the cell can no
longer divide successfully, and the cell
dies.
18. Chromosomal Abnormalities
The three major single-chromosome
mutations:
1. Deletion
2. Duplication
3. Inversion
The two major two-chromosome
mutations:
1. Insertion
2. Translocation
19.
20. Case: BCR-ABL1 Translocation
The Philadelphia chromosome or Philadelphia translocation (Ph) is a specific
genetic abnormality in chromosome 22 of leukemia cancer cells
(particularly chronic myeloid leukemia (CML) cells)
22. Chromosomal Karyotyping
• A karyotype test is a genetic test that checks the chromosomes in
your cells to:
- See whether you have a full set of 46 chromosomes. Having too many
or too few chromosomes can cause serious problems with health,
growth, and normal development, such as Down syndrome (extra
chromosome 21) and Turner syndrome (missing X chromosome).
- Look for changes in the structure of chromosomes, such as broken,
missing, or extra parts. These changes may cause a wide variety of
problems depending on which chromosome is affected. But some
changes in chromosomes don't cause problems.
Watch: https://www.youtube.com/watch?v=BbA-pHyirzo
23. Chromosomal Karyotyping
The slide is viewed by a light
microscope; the sample is seen on
a video screen. The chromosomes
can be arranged electronically
on the screen
For a diploid human cell, two complete sets of
chromosomes from a single cell constitute a
karyotype of that cell.
25. Cell Cycle
The cell cycle is the series of events that take place in a cell
leading to the duplication of its DNA and division.
Cell cycle has 4 main phases:
Interphase: A cell spends most of its time in this phase and
during this time it grows, replicates its chromosomes, and
prepares for cell division. This consists of 3 phases.
o G1 – cell growth
o S – DNA replication
o G2 – More cell division preparation
Cell division: Consists of 1 phase, M.
M phase includes mitosis and cytokinesis.
• Mitosis: Thecell then leaves interphase,
undergoes mitosis, and
completes its division. The resulting cells are known as
daughter cells.
• Cytokinesis: Cytokinesis is the physical process of cell division,
which divides the cytoplasm of a parental cell into two
daughter cells. It occurs concurrently with two types of
nuclear division called mitosis and meiosis, which occur in
animal cells.
26. Cell Cycle
• The cell cycle has 4 different phases called G1, S,
G2, and M.
• G1 is the stage where the cell is preparing to
divide. To do this, it then moves into the S phase
where the cell copies all the DNA. So, S stands for
DNA synthesis.
• After the DNA is copied and there's a complete
extra set of all the genetic material, the cell moves
into the G2 stage, where it organizes and
condenses the genetic material, or starts to
condense the genetic material, and prepares to
divide.
• The next stage is M. M stands for mitosis. This is
where the cell actually partitions the two copies of
the genetic material into the two daughter cells.
After M phase completes, cell division occurs and
two cells are left, and the cell cycle can begin
again.
Watch: https://www.youtube.com/watch?v=gTZ_vj-HdzM
