Transcript DNA
Biology Benchmark II Review DNA, Protein Synthesis, Genetics, Biotechnology DNA and Protein Synthesis DNA DNA • Double stranded • “Double Helix” • Four base pairs: ATGC • Sugar is Deoxyribose • Found in nucleus • Sides are built out of sugars and phosphates • Weak hydrogen bonds hold the base pairs together. Base Pair Rule • In DNA: Adenine always pairs with Thymine. Guanine always pairs with Cytosine. If one side of DNA is TCG GCA TCT, what is the complementary side? AGC CGT AGA Replication • Making of an identical strand of DNA • “semi” conservative because the two new DNA strands are half old and half new • DNA replicates during the S stage of the cell cycle Central Dogma DNA mRNA protein trait DNA vs. RNA DNA and RNA are similar because they are both types nucleic acids built out of nucleotides. But they have differences as seen in the chart below. Nucleic Acid Size Sugar Bases Location DNA Double stranded Deoxyribose ATCG In the nucleus RNA Single stranded Ribose AUCG Some kinds are in the nucleus, some are out in the cytoplasm There are 3 kinds of RNA • mRNA (messenger RNA) – carries the message of DNA from the nucleus out to the ribosome. • rRNA (ribosomal RNA) – makes up the ribosome and reads and decodes the mRNA calling out for particular amino acids. • tRNA (transfer RNA) – brings the amino acids to the ribosome and drops them off in the correct order so they can be joined to make the protein. Protein Synthesis occurs in two steps: • Transcription • Translation Transcription • DNA mRNA • Occurs in nucleus • Complementary mRNA strand is produced from a segment of DNA • Remember that every time you want to put a T you put a U instead If DNA has the sequence TCT GCA AAT, what would be the mRNA? AGA CGU UUA Translation • The ribosome connects amino acids (with peptide bonds) in the correct order to make a protein • Occurs in the cytoplasm within the ribosomes A- amino acid B- tRNA C- anticodon D- codon E- mRNA F- Ribosome G-polypeptide Codon • A codon is a sequence of three mRNA nucleotides that code for an amino acid What does mRNA ACU code for? Threonine What does DNA AGT code for? Serine Mutations • Change in DNA code • May cause a change in protein produced • NOT always harmful Sickle Cell Mutation Causes of Mutations • Point – just a single base is wrong. • Insertion or Deletion – you have extra or missing bases. This may lead to a frame shift mutation in which pretty much every single amino acid coded for is incorrect. • A mutation may be inherited from your parents or it may develop as a result to exposure to a mutagen like radiation or certain chemicals. Types of Cell Division: Mitosis and Meiosis Mitosis • Asexual cell division • Produces two identical diploid daughter cells • Occurs in body cells to grow and repair The Cell Cycle Mitosis • What is happening during G1, S, G2, and M? • The cell below is undergoing mitosis. What is happening to the chromosomes from one stage to the next? Cancer • Error in cell division resulting in uncontrolled growth. • Has environmental and genetic causes Meiosis • Cell division for the purpose of sexual reproduction. • Occurs in sex cells to form gametes • Produces four different haploid daughter cells (gametes) Notice the differences • How many cells do you get at the end of mitosis? How many chromosomes are in each cell compared to the original? • How many cells do you get at the end of meiosis? How many chromosomes are in each cell compared to the original? After MITOSIS you get 2 identical cells with the same number of chromosomes as the original. After MEIOSIS you get 4 different cells with half the number of chromosomes as the original. In meiosis, crossing over occurs • Homologous chromosomes exchange parts of their DNA • Creates variation in gametes • Crossing over is good because it leads to genetic variation In meiosis, nondisjunction can occur • Homologous chromosomes fail to separate during meiosis • Gametes have extra or missing chromosomes • Can lead to Down Syndrome • Nondisjunction is bad because it leads to eggs and sperm with the wrong number of chromosomes Asexual vs. Sexual Reproduction Asexual • One parent • Identical offspring • Variation only thru mutations • Examples: binary fission, budding, vegetative propagation • Mitosis is involved Sexual • Two parents • Offspring different from parents • More variation • Meiosis creates eggs and sperm • Once egg and sperm fertilize, mitosis is how the embryo grows Genetics Inheritance • Traits are specific characteristics inherited from parents • Genes are the factors that determine traits • Genes are on chromosomes • The different forms of a gene are called alleles Dominant/Recessive Alleles • Dominant alleles are expressed, if present, and recessive are hidden. Recessive traits only show if two recessive alleles are paired together. Genotype actual alleles an individual has for a trait Homozygous • Both alleles are the same • Ex. BB or bb Heterozygous • Both alleles are different • Ex. Bb Phenotype • The actual characteristic displayed by the individual (ex. brown eyes, Hemophiliac) You try one….. • In peas, tall is dominant to short. Cross a heterozygous tall pea with a short one. What percent of the offspring would be tall? 50% Incomplete Dominance • Heterozygote shows a blending of the dominant and recessive phenotypes • Red and white makes pink Codominance • Heterozygote expresses BOTH dominant and recessive traits • Ex. A white cow and a brown bull making a white and brown offspring Polygenic Traits • Traits are influenced by more than one gene • Ex. skin color Multiple Alleles • More than two alleles for a trait (an individual still only inherits two) • Ex. Blood Type (IA,IB, i) type A = IAIA or IAi type B = IBIB or IBi type AB= IAIB type O = ii Sex Linked Traits • Sex Chromosomes – Female = XX – Male = XY • Sex linked traits are carried on the X chromosome • Ex. Hemophilia, red-green colorblindness Test Cross • used to determine the phenotype of an unknown dominant looking individual • uses a homozygous recessive individual as the “test” • If any babies look recessive, your unknown dominant looking parent must have been heterozygous Pedigree • similar to a family tree in that it shows the pattern of inheritance of a specific trait through a family. • Circles are females, squares are males, colored in shapes are people with the disorder. Interpreting Pedigrees • Recessive diseases skip generations, dominant disease don’t. • Sex-linked diseases have more males with it. Autosomal diseases have about the same amount of males and females. • What is the inheritance pattern of the pedigree below? Sex-linked Recessive Karyotype • Picture of someone's chromosomes • Can detect chromosomal disorders like Down Syndrome, Klinefelter’s Syndrome, and Turner Syndrome Look at the karyotype on the right. Is this person male or female? Does this person have a problem? Down Syndrome female Some Diseases are Genetic Disease Inheritance Pattern Symptoms Cystic Fibrosis Autosomal Recessive Mucus clogs lungs PKU Autosomal Recessive Can’t break down phenylalanine, may have mental challenges if phenylalanine is present in diet Huntington’s Disease Autosomal Dominant Mood swings, seizures Sickle Cell Anemia Autosomal Recessive AA – Normal AS – Carrier SS – Sickle Cell Blood cells make a crescent shape *The sickle cell trait provides protection from malaria* Color Blindness Sex-Linked Recessive Can’t see certain colors Hemophilia Sex-Linked Recessive Blood doesn’t clot Genetic Disorders and the Environment • Many diseases have both genetic and environmental factors • Ex. Cancer, Type II diabetes, PKU, Cardiovascular disease Biotechnology Human Genome Project • Sequencing of human DNA so we know what genes are on what chromosomes and what gene sequences result in diseases • The knowledge is being used to develop gene therapies and to improve products humans use Gel Electrophoresis Making DNA fingerprint • Technique used to separate molecules based on their size. • Restriction enzymes are used to cut DNA into different sized fragments. • DNA is negatively charged and moves through the gel to the positive side. • Smaller fragments move farther through the gel. Who committed the crime below? Dino Identifying Parents • The child won’t match mom or dad exactly…..however, every band present in the child needs to have come from either the mother or the father. • Who are the parents of the soldier? Parents C and D Recombinant DNA • DNA that is a combination of DNA from different sources • Human insulin gene inserted into bacterial plasmid • Bacteria take in the recombinant plasmid • Bacteria are now able to produce human insulin Transgenic Organism • An organism with a gene from another source • used to improve food supply, research, and healthcare For example, Bt corn has a gene added from a bacteria. This causes pests to die when eating the plant. Clone • An organism made from one cell of another organism • A genetically identical copy – but will the clone be the same as the original? Probably not – environment plays a role in how an organism turns out. There are ethical, legal, and social issues resulting from our manipulation of DNA 1. 2. 3. 4. Who can afford gene manipulation? Will insurance companies drop coverage if they find out you have a disease? If we fix diseases, can the world support a growing population of people? Should people be able to design their babies?