BIO 101 Part B PDF

BIO 101 PART B COURSE OUTLINE Overview of the cell cycle The Chromosome The activities of chromosomes The phases of Mitosis and Meiosis Concepts of genotype and phenotype Law of independent assortment Law of Segregation  CELL CYCLE CELL: Is the basic membrane-bound unit that cont...

BIO 101 PART B COURSE OUTLINE Overview of the cell cycle The Chromosome The activities of chromosomes The phases of Mitosis and Meiosis Concepts of genotype and phenotype Law of independent assortment Law of Segregation  CELL CYCLE CELL: Is the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. Function of the cell Serves as the structural building block to form tissues and organs Each cell is functionally independent- it can live on its own under the right conditions It can define its boundaries and protect itself from external changes causing internal changes. It can use sugars to derive energy for different processes which keep it alive It contains all the information required for replicating itself and interacting with other cells in order to produce a multicellular organism It is even possible to reproduce the entire plant from almost any single cell of the plant  The cell cycle The cell cycle is a cycle of stages that cells pass through to allow them to divide and produce new cells. It is sometimes referred to as the “cell division cycle”. The cell division process is an integral part of the cell cycle, the life of a cell from the time it is first formed from a dividing parent cell until its own division into two daughter cells is essential for continuity of life. Passing identical genetic material to cellular offspring is a crucial function of cell division. Cell division plays several important roles in life. The division of one prokaryotic cell reproduces an entire organism. The same is true of a eukaryote. Cell division also enables multicellular eukaryotes to develop from a single cell, like the fertilized egg that gave rise to the two-celled embryo. And after such an organism is fully grown, cell division continues to function in renewal and repair, replacing cells that die from normal wear and tear or accidents. For example, dividing cells in your bone marrow continuously make new blood cells  The key functions of cell division 1. Reproduction: The ability of organisms to produce more of their own kind. In both prokaryotes and eukaryotes, most cell division involves the distribution of identical genetic material DNA to two daughter cells. During cell division the DNA is passed along from one generation of cells to the next. A dividing cell duplicates its DNA, allocates the two copies to opposite ends of the cell, and only then splits into daughter cells. E.g An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism  2. Growth and development: The cell cycle is used for growth and development of a single organism. 3. Tissue renewal: a cell exists through a preexisting cell. These dividing bone marrow cells will give rise to new blood cells.  Genome Genome: The genetic information of a cell is called its genome. It is the complete set of genetic information in an organism. It provides all of the information required by an organism to function. Although a prokaryotic genome is often a single DNA molecule, eukaryotic genomes usually consist of a number of DNA molecules. The overall length of DNA in a eukaryotic cell is enormous. A typical human cell, for example, has about 2 m of DNA a length about 250,000 times greater than the cells diameter. Yet before the cell can divide to form genetically identical daughter cells, all of this DNA must be copied, or replicated, and then the two copies must be separated so that each daughter cell ends up with a complete genome  The chromosome Chromosomes are the tread-like structures found in living cells that contain the genetic information of organisms. They contain the instructions for how an organism looks, how it develops and functions. Chromosomes are key components of a living organism and offer insight into how genes influence the development of an organism. Chromosomes are the smallest pieces of tissue in the body and are an integral part of passing on genetic information between generations. They are made up of DNA, which contain the code for the expression of all physical characteristics (e.g. height, eye color etc.) and other unique information that is passed down from ancestors to offspring, In other words, are the building blocks of life and are essential in maintaining the flow of hereditary traits and characteristics down through history.  Chromosome typically consisting of tightly wound strands of DNA and a proteins unit called histones. their role is to organize and condense the DNA tightly so that it fits into the nucleus The other proteins are enzymes used in copying and repairing the DNA. They are often referred to as the “building blocks of life” since they contain the genetic material or DNA which are inherited from ancestors and passed to the offspring. This molecular material is unique to each individual and contains important information such as eye color, age, sex and risk of developing specific diseases. Chromosomes act as the instructions for a developing embryo, providing for the growth and development of an individual throughout their life. Cats have 38 chromosomes Each species has a particular number of chromosomes that define their overall characteristics. For example, humans typically have 46 chromosomes in each cells, while cats have 38. Chromosomes are vital to cell development, allowing the specific genetic information of each organism to be inherited and species-specific traits to be expressed. For example, through the genetic material associated with specific chromosomes, humans can express features such as hair color, skin tone, and eye color. Chromosomes are essential to the growth and development of all organism, and are responsible for the unique features of each organism.  Structure of chromosome During interphase (S phase) the DNA replicates to create two identical strands of DNA called chromatids, joined together by a narrow region called the centromere The two chromatids that make up the double structure of a chromosome are known as ‘sister chromatids’ It is important that the sister chromatids are identical (contain the same genes) because this is key to cell division, as one chromatid goes into one daughter cell and one goes into the other daughter cell during mitosis, ensuring the daughter cells are genetically identical Each chromatid is made up of one very long, condensed DNA molecule, which is made up of a series of genes The ends of the chromatids in chromosomes are ‘sealed’ with protective structures called telomeres  Functions of chromosome 1.The most important function of chromosomes is to carry the basic genetic material – DNA. DNA provides genetic information for various cellular functions. These functions are essential for growth, survival, and reproduction of the organisms. 2.Histones and other proteins cover the Chromosomes. These proteins protect it from chemical (e.g., enzymes) and physical forces. Thus, chromosomes also perform the function of protecting the genetic material (DNA) from damage during the process of cell division. 3.During cell division, spindle fibers attached to the centromeres contract and perform an important function. The contraction of centromeres of chromosomes ensures precise distribution of DNA (genetic material) to the daughter nuclei. 4.Chromosomes contain histone and non-histone proteins. these proteins regulate gene action. Cellular molecules that regulate genes work by activating or deactivating these proteins. This activation and deactivation expand or contract the chromosome.  The DNA Structure The DNA structure can be thought of as a twisted ladder. This structure is described as a double-helix, It is a nucleic acid, and all nucleic acids are made up of nucleotides. The DNA molecule is composed of units called nucleotides, and each nucleotide is composed of three different components such as sugar, phosphate groups and nitrogen bases. The basic building blocks of DNA are nucleotides, which are composed of a sugar group, a phosphate group, and a nitrogen base. The sugar and phosphate groups link the nucleotides together to form each strand of DNA. Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) are four types of nitrogen bases. These 4 Nitrogenous bases pair together in the following way: A with T, and C with G. These base pairs are essential for the DNA’s double helix structure, which resembles a twisted ladder. Functions of the DNA DNA is the genetic material which car-ries all the hereditary information. Genes are the small segments of DNA, consisting mostly of 250 – 2 million base pairs. A gene code for a polypeptide molecule, where three nitrogenous bases sequence stands for one amino acid. Polypeptide chains are further folded in secondary, tertiary and quaternary structures to form different proteins. As every organism contains many genes in its DNA, different types of proteins can be formed. Proteins are the main functional and structural molecules in most organisms. Apart from storing genetic information, DNA is involved in: Replication process: Transferring the genetic information from one cell to its daughters and from one generation to the next and equal distribution of DNA during the cell division Mutations: The changes which occur in the DNA sequences Transcription Cellular Metabolism DNA Fingerprinting Gene Therapy  CELL DIVISION: Mitosis and Meiosis Prokaryotic cells, which include bacteria, undergo a type of cell division known as binary fission. This process involves replication of the cell's chromosomes, segregation of the copied DNA, and splitting of the parent cell's cytoplasm. The outcome of binary fission is two new cells that are identical to the original cell. In contrast to prokaryotic cells, eukaryotic cells may divide via either mitosis or meiosis. Of these two processes, mitosis is more common. In fact, whereas only sexually reproducing eukaryotes can engage in meiosis, all eukaryotes — regardless of size or number of cells — can engage in mitosis. But how does this process proceed, and what sorts of cells does it produce?  Phases of cell cycle MITOSIS mitosis, a process of cell duplication, or reproduction, during which one cell gives rise to two genetically identical daughter cells. The term mitosis is used to describe the duplication and distribution of chromosomes, the structures that carry the genetic information. Mitosis is common to all eukaryotes; during this process, a parent cell splits into two genetically identical daughter cells, each of which contains the same number of chromosomes as the parent cell. Mitosis is just one part of the cell cycle. The mitotic (M) phase, which includes both mitosis and cytokinesis, is usually the shortest part of the cell cycle. Mitosis is conventionally broken down into the following stages: 1. Interpahse, 2. prophase 3. prometaphase, 4. metaphase, 5. anaphase, 6. and telophase. Overlapping with the latter stages of mitosis, cytokinesis completes the mitotic phase.  Interphase interphase: Mitotic cell division alternates with a much longer stage called interphase, which often accounts for about 90% of the cycle. During interphase, a cell that is about to divide grows and copies its chromosomes in preparation for cell division. Interphase can be divided into subphases: the G1 phase ( first gap ), the S phase ( synthesis ), and the G2 phase ( second gap ). During all three subphases, a cell that will eventually divide grows by producing proteins and cytoplasmic organelles such as mitochondria and endoplasmic reticulum. However, chromosomes are duplicated only during the S phase. Thus, a cell grows (G1), continues to grow as it copies its chromosomes (S), grows more as it completes preparations for cell division (G2), and divides (M). A particular human cell might undergo one division in 24 hours. Of this time, the M phase would occupy less than 1 hour, while the S phase might occupy about 10 12 hours, or about half the cycle. The rest of the time would be apportioned between the G1 and G2 phases. The G2 phase usually takes 4 6 hours; G1 phase The first stage of interphase is called the G1 phase, or first gap, because little change is visible. However, during the G1 stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins, as well as accumulating enough energy reserves to complete the task of replicating each chromosome in the nucleus.  S phase (synthesis phase) Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration. In the S phase (synthesis phase), DNA replication results in the formation of two identical copies of each chromosome—sister chromatids—that are firmly attached at the centromere region. At this stage, each chromosome is made of two sister chromatids and is a duplicated chromosome. The centrosome is duplicated during the S phase. The two centrosomes will give rise to the mitotic spindle, the apparatus that orchestrates the movement of chromosomes during mitosis. The centrosome consists of a pair of rod-like centrioles at right angles to each other. Centrioles help organize cell division. Centrioles are not present in the centrosomes of many eukaryotic species, such as plants and most fungi. G2 phase In the G2 phase, or second gap, the cell replenishes its energy stores and synthesizes the proteins necessary for chromosome manipulation. Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic spindle. There may be additional cell growth during G2. The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis. In summary, at interphase: It is a preparatory stage Respiration, protein synthesis, growth occurs Genetic material is duplicated (DNA replicates) itself Cells usually small with no large vacuoles  prophase The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope. The nucleoli disappear. Each duplicated chromosome appears as two identical sister chromatids joined at their centromeres and, in some species, all along their arms by cohesins (sister chromatid cohesion). The mitotic spindle (named for its shape) begins to form. It is composed of the centrosomes and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters ( stars ). The centrosomes move away from each other, propelled partly by the lengthening microtubules between them. In summary at prophase : 1. Nuclear envelope disappears 2. Nucleolus disappears 3. Chromatin condenses (shortens and thickens) to become chromosomes 4. Later, spindle starts to form (spindle composed of microtubules - like muscles) Prometaphase The nuclear envelope fragments. The microtubules extending from each centrosome can now invade the nuclear area. The chromosomes have become even more condensed. Each of the two chromatids of each chromosome now has a kinetochore, a specialized protein structure at the centromere. Some of the microtubules attach to the kinetochores, becoming kinetochore microtubules, which jerk the chromosomes back and forth. Nonkinetochore microtubules interact with those from the opposite pole of the spindle. Metaphase The centrosomes are now at opposite poles of the cell. The chromosomes convene at the metaphase plate, a plane that is equidistant between the spindle s two poles. The chromosomes centromeres lie at the metaphase plate. For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles. In summary at metaphase: 1. Chromosomes line up on equator 2. Each centromere attached to spindle fiber 3. Very end of metaphase - centromeres divide  Anaphase Anaphase is the shortest stage of mitosis, often lasting only a few minutes. Anaphase begins when the cohesin proteins are cleaved. This allows the two sister chromatids of each pair to part suddenly. Each chromatid thus becomes a full- edged chromosome. The two liberated daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere rst (at about 1 m/min). The cell elongates as the nonkinetochore microtubules lengthen. By the end of anaphase, the two ends of the cell have equivalent and complete collections of chromosomes. In summary at anaphase 1. Sister chromatids are pulled to opposite end of cell by contraction of spindle fibers 2. Each chromatid is now considered one chromosome (a) Metaphase and (b) Anaphase. In metaphase (a), the microtubules of the spindle (white) have attached and the chromosomes have lined up on the metaphase plate. During anaphase (b), the sister chromatids are pulled apart and move toward opposite poles of the cell. Telophase Two daughter nuclei form in the cell. Nuclear envelopes arise from the fragments of the parent cells nuclear envelope and other portions of the endomembrane system. Nucleoli reappear. The chromosomes become less condensed. Any remaining spindle microtubules are depolymerized. Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete. In summary at Telophase (reverse of prophase) 1. Nuclear envelops reforms (2) 2. Chromosomes lengthen and become indistinct (chromatin) 3. Nucleolus reappears Cytokinesis The division of the cytoplasm is usually well under way by late telophase, so the two daughter cells appear shortly after the end of mitosis. In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two. IN SUMMARY Importance of Mitosis As mentioned earlier, most eukaryotic cells that are not involved in the production of gametes undergo mitosis. These cells, known as somatic cells, are important to the survival of eukaryotic organisms, and it is essential that somatic parent and daughter cells do not vary from one another. With few exceptions, the mitotic process ensures that this is the case. Therefore, mitosis ensures that each successive cellular generation has the same genetic composition as the previous generation, as well as an identical chromosome set.