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DNA and Protein Synthesis

DNA and Protein Synthesis. Week 8. DNA. DNA- deoxyribose nucleic acid – molecule that stores the information that controls a cell’s function. The larger a cell becomes, the more demands the cell places on its DNA.

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DNA and Protein Synthesis

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  1. DNA and Protein Synthesis Week 8

  2. DNA • DNA- deoxyribose nucleic acid – molecule that stores the information that controls a cell’s function. • The larger a cell becomes, the more demands the cell places on its DNA. • DNA is found in eukaryotic nuclei. As the cell grows, it does not create extra copies of DNA. There becomes an “information crisis.” • Eventually, the cell would no longer be able to serve the increasing needs of the growing cell.

  3. Cell Division • The first stage of cell division is mitosis, or the division of the nucleus. The second step is cytokinesis, or the division of the cytoplasm. • Chromosomes carry genetic information from one generation to the next. • Chromosomes are made up of DNA and proteins. Each organism has a specific number of chromosomes. (Fruit flies- 8; carrots- 18; humans-?) • Chromosomes are not visible except during cell division. DNA and protein are spread throughout the nucleus.

  4. Cell Division • In preparation for cell division, each chromosome is replicated. Each chromosome then consists of two identical chromatids. They then separate, one to each cell. • Centromeres are the areas where chromatids attach.

  5. Interphase • Interphase – the in-between period of cell growth • During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again. • G1 phase is when the cell grows • S phase is the time when the DNA replication takes place. • G2 phase is the final preparation for division, including the production of organelles needed.

  6. Prophase • Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and telophase. • Prophase is the first and longest phase of mitosis. It can take up 50-60% of the total time required. • Chromosomes become visible.

  7. Prophase • Centrioles separate and take up positions on opposite sides of the nucleus. • The centrioles lie in a region called the centrosome that helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes. • Near the end of the prophase, the chromosomes coil more tightly, the nucleolus disappears, and the nuclear envelope breaks down.

  8. Metaphase • Metaphase is the second phase of mitosis, and only lasts a few minutes. • Chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the two poles of the spindle.

  9. Anaphase • Anaphase is the third phase of mitosis. • The sister chromatids separate and become individual chromosomes. • The chromosomes continue to move until they have formed two groups near the poles of the spindle. • Anaphase ends when the chromosomes stop moving.

  10. Telophase • Telophase is the fourth and final phase of mitosis. • The chromosomes begin to disperse into a tangle of dense material. • A nuclear envelope re-forms around each cluster of chromosomes, the spindle breaks apart, and a nucleolus becomes visible in each.

  11. Cytokinesis • Cytokinesis usually occurs at the same time as telophase. The cytoplasm of the cell is pinched into two nearly equal halves, or a cell wall forms between the divided nuclei.

  12. Transformation • Griffith investigated how certain types of bacteria produce pneumonia. He isolated two strains, one that caused the disease and one that would not. • In his experiments, he discovered that heat-killed, disease causing bacteria would not cause pneumonia. However, when he mixed this heat-killed bacteria with non-disease causing bacteria, he found that pneumonia developed. (Neither type caused pneumonia by itself.) • Somehow, the harmless strain acquired something from the disease causing strain. Griffith called this process transformation.

  13. Transformation • Avery and his colleagues repeated Griffith’s work. • They made an extract from the heat-killed bacteria, and then treated the extract with enzymes to destroy proteins, lipids, carbohydrates, and other molecules, including RNA. Transformation still occurred. • They then tried enzymes that would destroy DNA, and the transformations stopped. • Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

  14. DNA • A bacteriophage is a virus that infects bacteria. It is composed of a DNA or RNA core and a protein coat. • Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein. • DNA is made of nucleotides. Nucleotides are made up of a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base. • There are four kinds of nitrogenous bases: adenine, guanine, cytosine and thymine.

  15. DNA • Chargaff’s Rules- [A] = [T] and [G] = [C] • Franklin’s X-ray diffraction images of DNA carried important clues to the structure. • Watson and Crick’s model of DNA was a double helix, in which two strands were wound around each other. • Base pairing, along with the double helix model, explained Chargaff’s Rules. • DNA molecules are surprisingly long.

  16. DNA • Eukaryotic chromosomes contain DNA and protein tightly packed together to form chromatin, which is tightly coiled around proteins called histones. • Because of base pairing, DNA can split down the middle, and still know how to reconstruct the missing side. • During DNA replication, the DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template for the new strand. • Replication is helped by the enzyme DNA polymerase. • Genes are coded DNA instructions that control the production of proteins within the cell.

  17. RNA • There are three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA. • messenger RNA (mRNA) carries copies of the instructions for assembling amino acids. • ribosomal RNA (rRNA) help make up ribosomes, where proteins are assembled. • transfer RNA (tRNA) moves each amino acid to the ribosome.

  18. RNA • Transcription is a process where RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence of RNA, using RNA polymerase. • During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA. • A codon is the three-letter “word” of genetic code.

  19. Codons • For example, a line of RNA sequence would be: • UCGCACGGU • Break the sequence to 3 letter “words”: • UCG-CAC-GGU • The words mean: • Serine-Histidine-Glycine • AUG=Methionine or START • UAA, UAG, or UGA means STOP

  20. Mutations • During translation, the cell uses information from messenger RNA to produce proteins. • Mutations are changes in the genetic material. • A point mutation involves changes in one or a few nucleotides at a single point. • If a nucleotide is added or deleted, the groupings are shifted, and are called frameshift mutations. • Chromosomal mutations involve changes in the number or structure of chromosomes.

  21. Genes • The lac genes are turned off by repressors and turned on by the presence of lactose. • Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon. • Differentiation means that cells become specialized in structure and function.

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