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Cells Part II - DNA& Cell Division Nucleic Acids •...

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Unformatted text preview: DNA & Cell Division Nucleic Acids • Polymers of monomers called nucleotides • serves as blueprint for protein synthesis • two types of nucleic acids – DNA (deoxyribonucleic acid) • contains all the inheritable genetic information (genes) – RNA (ribonucleic acid)­ involved in protein synthesis • mRNA • rRNA • tRNA Nucleotide • Each nucleotide has three parts – sugar­ ribose (5C sugar) or deoxyribose – phosphate group­ constant – nitrogenous base­ variable OH or H 5 different kinds of bases classed into two groups DNA and RNA are Different O 5’ OH P O O Base Base 5’ CH 2 OH O P O CH 2 O 3’ 3’ OH H OH OH A,C,G,T A,C,G,U Double Stranded Long Single Stranded Short Double Stranded DNA DNA Strand With Complimentary Base Paring Complimentary Base Pairing Organization of Genetic Material • DNA in the cell is thick and very long when compared to the size of the nucleus – Perspective: if a DNA molecule was the thickness of a telephone pole, it would reach 2700 miles into space • The cell has 46 DNA molecules that must fit into the nucleus organized and intact. Organization of Genetic Material • Chromatin­ longs strands of DNA in beaded like strands • Nucleosome­ DNA wrapped around a cluster of proteins called histones • Non­histons protein­ provide structural support for the chromatin and help regulate gene activity Nucleosome DNA Replication In Cell Division The reasons for cell division • growth • repair • reproduction Two kinds of cell division • somatic cell division­ mitosis • sex cell division­ meiosis DNA Replication Replication begins at a Specific Sight on the Double Helix Daughter strand synthesized continuously 3’ 5’ 3’ DNA Polymerase Linking nucleotides proof reading repairing DNA 3’ 5’ 3’ 3’ 3’ 3’ 3’ 3’ 3’ DNA Ligase DNA repair Daughter strand synthesized in segments 5’ Semiconservative Replication The DNA Genotype is Expressed as Proteins, Which Provide the Molecular Basis for Phenotypic Traits One Gene One Enzyme Hypothesis Genetic Information is Written as Codons and Translated into Amino Acid Sequences Triplet Code Genetic Code 64 Codes for amino acids Redundancy From DNA to Proteins Transcription of a Gene Promoter­ a nucleotide sequence located next to the gene that signals the “start transcribing point”. Transcription divided into 3 phases Initiation­ occurs when RNA polymerase attaches to the promoter DNA. Elongation­ elongation of the RNA template Termination­ a special DNA sequence (terminator) that signal to RNA polymerase to stop transcribing and leads to its detachement from the RNA molecule and gene. Genetic Messages are Translated in the Cytoplasm Machinery required for Translation •Transfer RNA •Ribosomes ­ organelles where polypeptide synthesis occurs •Enzymes ­ a number of protein factors •Chemical energy ­ ATP Transfer RNA Molecule Serve as Interpreters During Translation tRNA Molecules must carry out two distinct functions • Picking up the appropriate amino acids •Recognizing the appropriate codons in mRNA There is also a family of enzymes that insures the proper amino acid is attached to the right tRNA. •There is a different enzyme for each amino acid . Binding Sites of the Ribosome RNA (rRNA) Large subunit Small Subunit Translation can be dividedinto the same there phases as transcription • initiation • elongation • termination Each a.a. addition occurs in a three­step elongation process • codon recognition • peptide bond formation • translocation Mutations • Any change in the nucleotide sequence of DNA • Three major types of mutations • alterations within a gene • abnormal numbers of chromosomes – too many or too few of a certain chromosome • abnormal chromosome structure – breakage leading to rearrangements Mutation (continued) • Alterations within a gene – base substitutions­ the substitution of one nucleotide for another Normal Gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly Ala A U G A A G U U U A G C G C A Met Lys Phe Ser Ala Base Substitutions • Depending on how a base substitution is translated, it can result in – no change in the protein – in a insignificant change – in a change that might be crucial to life (sickle cell anemia) – occasional improvement that enhance the survival of the organism • Some substitutions have no effect due to redundancy of the genetic code Mutation (continued) • Alterations within gene – base deletions and insertions­ are often disastrous due to the alteration of the reading frame – all nucleotides down stream from the mutation will be regrouped into different codons Base Insertions or Deletions Normal Gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly Ala U A U G A A G U U G G C G C A U Met Lys Leu Ala His Mutagenesis • The process of creating a mutation • Spontaneous mutations­ mutations resulting from errors during DNA replication or recombination and mutations of unknown cause • Mutagens­ the source of a mutation – can be physical, chemical agents, or biological Mutagenesis • Certain mutagens that are cancer causing are called Carcinogens – physical agents • high energy radiation is the most common physical agent • ultraviolet radiation Mutagenesis • Chemical agents – tobacco­ known to cause more cases and types of cancer than any other single agent • cancer of the lung, bladder, kidne, mouth and throat, pancreas,stomach, and cervix – alcohol • cancer of the mouth and throat, and liver • Biological agents – viruses • cancer of the cervix, liver, and blood Point Mutation in Sickle Cell Anemia • The effects of sickle cell anemia vary from one person to another, ranging from mild to severe symptoms. However the basic problem is the same­­the sickle cell shaped red blood cells block narrow blood vessels and impede the flow of blood. • Sickle Cell Crisis: Sickle cell crisis refers to a sudden increase of anemia, pain, fever, and sometimes shortness of breath. This is can be caused by anything that reduces the amount of oxygen in the blood, such as vigorous exercise, high altitudes, or illness. – Anemia: Because of the reduction in oxygen transport, people may feel fatigued, become pale or short of breath. – Pain: Pain can occur unpredictably in any body organ or joint, wherever the sickle shaped blood cells block oxygen flow to the tissues. Pain often occurs in the long bones and abdomen, sometimes severe enough to induce vomiting. – Jaundice: Yellowing of the skin and eyes due to the rapid breakdownof red blood cells. – Infections: Sickled cells cause damage to the spleen and prevent the spleen from destroying bacteria in the blood. Because the spleen helps fight infection, affected people are more likely to develop pneumococcal pneumonia and other infections. – Stroke: The defective hemoglobin damages the membranes of the red blood cells, causing them to stick to blood vessel walls. This can result in narrowed or blocked vessels in the brain and lead to a stroke. – Acute Chest Syndrome: In children, sickle cell crisis may include severe chest pain and difficulty in breathing. The cause of the chest syndrome is unknown but is thought to be the result of blocked vessels. – Hand­foot Syndrome: Poor circulation to the small blood vessels of the skin of the extremities may cause tissue damage. This may manifest as pain, swelling, or sores. Exchange Transfusion Somatic Cell Division Includes all body cells except the sex cells • cell division is for growth and repair • starting cell (parent cell) divides to produces two identical cell (daughter cells) • the process of division is called mitosis Mitosis • all somatic cells contain 46 chromosomes (23 pairs homologous pairs) • cell must duplicate all genetic material and organelles Cell Cycle Cell Cycle • The length of the cell cycle varies greatly from one cell type to another – Stomach and skin divide rapidly, whereas bone and cartilage slowly, and muscle and nerve cell, not at all – G0­ when the cell ceases to divide to enter a “rest” phase (may last for years) Interphase In “S” Phase of the Cell Cycle, the DNA Replicates Prophase Metaphase Astral rays Mitosis • The centromere joins the two sister chromatids. • During mitosis a protein structure called a Kinetochore forms on each side of the centromere. • The spindles attach to the Kinetochore. • The spindles then pull the sister chromosomes apart. Anaphase Telophase/Cytokinesis Transcription Translation Genetic Code •Signal peptide­ determines the protein’s destination •Posttranslational modification­ removing some amino acids segments, folding the protein and stabilizing it with disulfide bridges, adding carbohydrate moities, etc. ...
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