FCH 532 Lecture 1: intro to DNA and genetics

FCH 532 Lecture 1: intro to DNA and genetics Webpage: http://www.esf.edu/chemistry/nomura/fch532/ Genetics review Chapter 1

Figure 2.1 The storage and replication of biological information in DNA and its transfer to RNA to synthesize proteins that direct cellular function. Molecules that carry cellular information/instructions: DNA RNA Proteins Carbohydrates Lipids/fatty acids

Expression and Transmission of Genetic Information • Deoxyribonucleic acid (DNA) is the master template for genetic information. • Consists of two strands of linked nucleotides • Nucleotides are composed of • Deoxyribose sugar • Phosphoryl group • One of four bases: Adenine (A), Thymine (T), Guanine (G), or Cytosine (C). • Genetic information is encoded in the sequence of the nucleotides.

Figure 1-16 Double-stranded DNA. • Each DNA base is hydrogen bonded to a base on the opposite strand forming a base pair. • A bonds with T and G bonds with C forming complementary strands. Page 18

Figure 1-17 Schematic diagram of DNA replication. • The division of a cell must be accompanied by replication of DNA • Enzymatically catalyzed • Each DNA strand acts as a template for its complementary strand. • Each progeny cell has one parental strand and one daughter strand. • Mutations occur in copying errors or damage to a parental strand-causes one or more wrong bases to be incorporated into the daughter strand • Most mutations are innocuous or deleterious. Page 18

Expression of Genetic Information • Expression of genetic information takes place in two-stages. • Stage I: Transcription: DNA strand serves as a template for the synthesis of a complementary, single-strand of ribonucleic acid (RNA). RNA has ribose instead of deoxyribose (Ch 5) and uracil (U) replaces thymine (T). • Stage II: Translation: Ribosomes translate the RNA sequence to enzymatically assemble amino acids to form polypeptides. DNA  RNA  Protein

Cells store genetic information in double-stranded DNA • Double-stranded DNA is the carrier of genetic information in all cells and most viruses. • Viruses are extracellular packages of genetic information-can store their genetic information in double-stranded DNA, double-stranded and single-stranded RNA, and single-stranded DNA. • Cellular DNA duplexes are organized into chromosomes.

Circular chromosomes • Procaryotic chromosomes contain a single circular DNA duplex. • Procaryotes are haploid (1N) meaning that they have a single copy of their genetic information. • Many procaryotes also have small, autonomous, circular DNA duplexes called plasmids. • Chromosomal DNA is complexed with basic proteins and RNA molecules that fold it into a semi-condensed state (nucleoid). • Mitochondrial and chloroplast DNAs are also circular.

Linear chromosomes • Eucaryotic genomes are composed of several linear DNA duplexes that are organized into several chromosomes within the nucleus. • Consist of long continuous DNA molecule associated with small basic proteins called histones. • In eukarotic cells, there are normally two copies of each chromosome (homologous pairs) in every somatic cell.

Figure 1-18 Chromosomes. Page 19

Eukaryotic cells • Realization that all organisms are derived from single cells set the stage for the development of modern biology. • Germ cells (sperm and ova) are directly descended from germ cells of the previous generation. • Somatic cells (all other cells) are derived from germ cells but do not give rise to them. • Most eukaryotes are diploid (2N) meaning they have two homologous sets of chromosomes, one from the female parent and one from the male parent.

Table 1-2 Number of Chromosomes (2N) in Some Eurkaryotes. Page 19

Figure 1-19 Mitosis, the usual form of cell division in eukaryotes. • Somatic cells divide by mitosis. • 2N duplicates to 4N and results in two daughter cells with 2N • During cell division, each chromosome attaches by its centromere to the mitotic spindle. • Members of each are pulled to opposite poles of the dividing cell by the spindle to yield diploid daughter cells. Page 20

Figure 1-20 Meiosis, which leads to the formation of gametes (sex cells). • Germ cells are formed by meiosis. • Requires 2 cell divisions. • Before the first meiotic division, each chromosome replicates but the resulting chromatids are attached to the centromere. • Recombination can occur between sections of homologous chromosomes during metaphase I (crossing-over). • Results in four haploid cells (gametes). Page 21

Genetics and inheritance • 1st reported by Gregor Mendel in 1866, he analyzed a series of genetic crosses between garden peas. • Characterized differences in physical traits: seed shape (round vs. wrinkled), seed color (yellow vs. green) or flower color (white vs. purple). • Findings: crossing parents (P generation) with two different traits results in progeny (F1-first filial generation) that are similar to one of the parents. • The trait appearing in the F1 generation is considered to be dominant and the alternate trait is said to be recessive. • If the F1 generation are crossed the resulting F2 generationare 3/4 dominant and 1/4 recessive.

Figure 1-21 Genetic crosses. Page 21

Genetics and inheritance • If the F2 generation with the recessive traits are crossed, all of the progeny will show the recessive trait. • The F2’s showing a dominant trait fall into 2 categories: 1/3 breed true, whereas the remaining 2/3 fall into the same 3:1 ratio of dominant to recessive traits. • These are accounted for from genes with alternative forms (alleles). • Each plant has a pair of genes that code for each trait. One gene each is inherited from each parent. • Example RR for round seeds and rr for wrinkled seeds-genotypes. • These are called homozygous for seed shape in genotype. • Plants with the Rr genotype are heterozygous for seed shape and have the round phenotype.

Figure 1-22 Genotypes and phenotypes. Page 22

Figure 1-23 Independent assortment. • Some different traits are independently inherited. • Here 2 sets of alleles are responsible for the phenotypes: R for round, r for wrinkled, Y for yellow, and y for green. Page 22

Figure 1-24 Codominance. • Some instances when the dominance of both traits are equal. • In snapdragons a pure red (AA) is crossed with a pure white (aa) to yield and F1 generation that is pink (Aa). • Crossing the F1 generation results in a 1:2:1 ratio of red:pink:white. • Codominance. Page 23

Figure 1-25 Independent segregation. • Chromosomal theory of inheritance-genes are parts of chromosomes. • First trait to be assigned chromosomal location: sex • Females: 2 copies of the X chromosome (XX). • Males have the Y chromosome (XY). • Explains the 1:1 ratio of males to females in most species. • X and Y chromosomes are referred to as sex chromsomes. Page 23

Figure 1-26 The fruit fly Drosophila melanogaster. • Produce new generation every 14 days so genetic crosses can be seen faster than with peas. • 1st mutant strain had white eyes instead of red eyes of the wild type (occuring in nature). Through genetic crosses it was shown that the white eye gene (wh) parallels the X chromosome. This means the wh gene is located on the X chromosome and the Y chromosome does not contain it. • Sex linked chromosome. Page 23

Figure 1-27 Crossing-over. • Genes that are on the same chromosome do not sort independently. • However, linked genes recombine (exchange relative positions with their allelic counterparts on homologous chromsomes) with a certain characteristic frequency. • Occurs in the start of meiosis (metaphase I) • Can be used to map relative positions on different chromosomes. Page 24

Figure 1-28 Portion of the genetic map of chromosome 2 of Drosophilia. • Two genes separated by m map units recombine with a frequency of m%. Page 25

Nonallelic genes complement one another • To examine whether or not 2 recessive that traits affect similar functions are allelic (different forms of the same gene) you can do a complementation test. • Homozygotes for both traits to be tested are crossed to each other. • If the traits are nonallelic, the progeny will have the wild-type phenotype since the two genes complement one another. • If not, then the genes are allelic.

Figure 1-29a The complementation test indicates whether two recessive traits are allelic. (a) Crossing a homozygote for purple eye color with a homozygote for brown eye color. Page 25

Figure 1-29b The complementation test indicates whether two recessive traits are allelic. (b) Crossing a female with white eye color gene with a male with coffee eye color gene. Page 25

FCH 532 Lecture 1: intro to DNA and genetics