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Lecture 6


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Lovaye Kajiura

Oct. 7, 2013 Icliker questions 1) Chitin differs from another long chain polysaccharide, cellulose, in that the former has what unique functional group? • B) Nitrogen containing functional group 2) Which part of DNAnucleotide below is different from the analogous nucleotide in RNA? • B) Sugar 3) Acells membrane is not formed properly – it is not able to act as a barrier to its environment. What may be a main cause of this problem? • B)The ER is malfunctioning and cannot produce the phospholipids and cholesterol for the membrane. 4) In the figure below, what is the correct association? (Picture of a caribou) difference between trunk and legs • D) Leg lipids: unsaturated fatty acids 5) Is asexual reproducton used by all organisms including humans? • Yes.Although humans reproduce via sexual reproduction our body(somatic) cells propagate asexually 6)Which of the following does not describe sister chromatids • They separate centromeres 7) You can tell the difference between a plant cell and an animal cell undergoing cytokinesis because • the plant cell has a cell plate; the animal cell has cleavage now Biology Week 6 Lecture Notes Chapter 9 – The Continuity of Life Cellular Reproduction Why is cell division IMPORTANT for eukaryotic organisms? CELL DIVISION: is required for growth, development and repair • transmits hereditary information from parents cells to the daughter cells • is required sexual and asexual reproduction Where is the information found in the parental cells? • The info. Is encoded in the DNAthat contain the genes How is the DNAin eukaryotic cells organized? • Eukaryotic chromosome consists of DNAbound to proteins • duplicated chromosomes separate during cell division • eukaryotic chromosomes usually occur in pairs (homologous) What is a Karyotype? • Organized display of the homologous pairs of chromosomes and the sex chromosomes • Two types of cell division in Eukaryotic Cells MITOTIC cell division MEIOTIC cell division – variation What are the underlying cause of CANCER? • Cancer is unregulated and uncontrolled cell division • that is the reason why our understanding of the cell cycle is so important (i.e significance) Why do cells divide? • Rudolf Virchow – 1800s captured the critical importance of cellular reproduction for all living organisms • Cells reproduce by cell division in which a parent cell usually produces two daughter cells ◦ each daughter cell receives a complete set of hereditary information, identical to the hereditary information of the parent cell and about half the parents cell's cytoplasm • Cell division transmits hereditary information to each daughter cell • Hereditary information of all living cells in contained in deoxyribonucleic acid (DNA) ◦ DNAis a polymer composed of subunits called nucleotides ◦ Each Nucleotide consists of a phosphate a sugar (deoxyribose) and one of the four bases – adenine (A), thymine (T), guanine (G) or cytosine (C) • Achromosome consists of DNAwith proteins that organize its three dimensional structure ◦ consists of two long strands of nucleotides wound around each other (like a ladder would look if twisted); called double helix • Units of inheritance, genes, are segments of DNAranging from a few hundred to many thousands of nucleotides – the specific sequences of nucleotides in genes spell out instructions for the proteins of a cell • For a cell to survive must have a complete set of instructions – that's why when a cell splits during cell division, the cell splits its genes in half and give each daughter cell a half of the set Cell division is required for growth and development • after cell division the daughter cells may grow and divide again or they may differentiate becoming specialized for specific functions such as contraction (muscle cells), fighting infection (white blood cells) etc • Cell Cycle – repeating pattern of divide and differentiate then divide again process • Three categories of cells based on their abilities to divide and differentiate ◦ Stem Cells – most of the cells formed by the first few cell divisions of a fertilized egg and a few cells in adults including cells in the heart, skin, intestines, fat, brain and bone marrow ◦ Self renewal means that stem cells react the capacity to divide perhaps for the entire life of the organism ◦ Usually when a stem cell divides one of its daughters remains a stem cell maintaining the population of stem cells; The other cell undergoes several rounds of cell division but resulting cells eventually differentiate into specialized cell type ◦ (ability to differentiate into a variety of cell types) ◦ Other Cells Capable of Dividing – Many cells of the bodies of embryos, juveniles and adults can also divide but each type of cell can typically differentiate into only one or two different cells types ◦ Permanently Differentiated Cells – Some cells differentiate and never divide again. For example most of the cells in your heart and brain cannot divide Cell division is required for sexual and asexual reproduction • Sexual reproduction in eukaryotic organisms occurs when offspring are produced by the fusion of gametes (sperm and eggs) generated in the gonads of adults • Meiotic cell division produces daughter cells with exactly half of the genetic information of the parent cells; daughter cells become sperm of eggs – when a sperm fertilizes an egg the resulting offspring containing all the genetic information • Asexual reproduction produces offspring that are genetically identical to the parent and to each other they are clones • Bacteria and many single celled eukaryotic organisms (i.e Paramecium) reproduce asexually by cell division in which two new cells arise from each preexisting cell • Some multicellular organisms can also reproduce asexually ◦ Example: Hydra reproduces by budding – grows a replica of itself called a bud; eventually the bud is able to live independently and separates from its parent forming a new Hydra What occurs during the prokaryotic cell cycle • Prokaryotic cell cycle consists of a relatively long period of growth – during which the cell replicates its DNA– followed by a type of cell division called prokaryotic fission • The prokaryotic chromosome is usually attached to the inside of the plasma membrane of a cell(1) ◦ During the growth phase of the prokaryotic cell cycle, the DNA is replicated producing two identical chromosomes that become attached to the plasma membrane nearby but separate, sites. (2) ◦ Anew plasma membrane is added between the attachment sites of the chromosomes, pushing them apart.(3) ◦ When the cell has doubled in size the new plasma membrane around the middle of the cell grows inward between the two attachment sites (4) ◦ The plasma membrane then fuses along the equator of the cell producing two daughter cells each consisting one of the chromosomes (5) ◦ Produces two identical daughter cells How is the DNAin Eukaryotic chromosomes organized ? • Eukaryotic chromosomes differ from prokaryotic chromosomes in that they are separated from the cytoplasm in a membrane-bound nucleus. • Eukaryotic cells have multiple chromosomes • Eukaryotic chromosomes contain more DNAthan prokaryotic chromosomes The Eukaryotic Chromosome consists of a linear DNADouble Helix bound to Proteins • For most of a cell's life the DNAin each chromosome is wrapped around proteins called histones (1 – A Eukaryotic chromosome contains a single DNA double helix; 2 – The DNA is wound around proteins called histones reducing the length by about a factor of 6) • The DNA/histone beads further coil up like a spring or Slinky toy(3 – Other proteins coil up the DNA/histone beads) reducing length again by 6 or 7) and then these coils are bent by attaching them to “scaffolds” made of additional proteins th • All this wrapping condenses the DNAto about 1/1000 of its original length(4)\(Condense even more during cell division) • Genes are segments of the DNAof a chromosome ◦ each gene occupies a specific place of locus (loci = plural) (Humans contains few as 70 genes to over 3000) • Specialized regions that are crucial to its structure and function – two telomeres and one centromere • Telomeres are protective caps at each end of a chromosome -w/o these genes at the end of the chromosomes would be lost during DNAreplication; also keep chromosomes from fusing with one another • Centromere – temporarily holds two daughter DNAdouble helices together after DNA replication and it is the attachment site for microtubules that move the chromosomes during cell division • Duplicated Chromosomes consist of two identical DNAdouble helices now called sister chromatids which are now attached to which other at the centromere • the entire set of chromosomes from a single cell is called its karyotype ◦ a karyotype consists of pairs of chromosomes; the two chromosomes that make up a pair are called homologous chromosomes or homologous ◦ Cells with pairs of homologous chromosomes are diploid meaning double ◦ Atypical human cell is diploid with 23 pairs of chromosomes for a total of 46 ▪ Fig 9-6: Staining and photographing the entire set of duplicated chromosomes from a
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