Topic 3_Nuclear Structure and Function_NMU.pdf
- 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.
- 13. Eukaryote vs Prokaryote: Chromosomal Structure Differences
- 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
- 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.
- 24. Chromosome Karyotyping in Cancer Cells
- 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