Scientific Basis of Genetics Janice S. Dorman, PhD University of Pittsburgh School of Nursing

Lessons Cell cycle Transcription Chromosomes Translation DNA and RNA Structure of a gene Transcription Translation Mutations

Lesson One Cell Cycle

The eukaryotic cell cycle The eukaryotic cell cycle. Cells that are destined to divide progress through a series of stages, denoted G1, S, G2, and M phases (mitosis). This diagram shows the progression of a cell through mitosis to produce two daughter cells. The original diploid cell had two pairs of chromosomes, for a total of four individual chromosomes. During S phase, these have replicated to yield eight sister chromatids. After mitosis is complete, there are two daughter cells each containing four chromosomes.

Mitosis Somatic cells divide by mitosis Involves 1 cell cycle / division Parental and 2 daughter cells are genetically identical Parental cells are diploid (46 chromosomes) 2 daughter cells are diploid (46 chromosomes)

Meiosis Germ cell precursors (parental cells) divide by meiosis Involves 2 cell cycles / divisions instead of 1 Germ cells precursors and 4 gametes (daughter cells – either egg or sperm) are NOT genetically identical Germ cell precursors are diploid (46 chromosomes) 4 gametes are haploid (23 chromosomes)

The stages of meiosis in an animal cell

The stages of meiosis in an animal cell Recombination occurs here The stages of meiosis in an animal cell

The stages of meiosis in an animal cell

Lesson Two Chromosomes

Chromosome Structure Chromosomes have 2 arms that are separated by the centromere: p arm – for petite q arm – long arm Ends of chromosomes are called telomeres

The steps in eukaryotic chromosomal compaction leading to the metaphase chromosome. The DNA double helix is wound around histone proteins and then further compacted to form a highly condensed metaphase chromosome

Chromosome Types Autosomes: the numbered chromosomes All individuals have 2 copies of each type of autosome (homologous chromosomes – 1 maternal, 1 paternal) Sex chromosomes: the X and Y chromosomes All individuals have 2 sex chromosomes XX = female XY = male

Karyotype An organized picture of the chromosomes found in a cell Captured during mitosis, just before cell divides Generally demonstrates the normal complement of chromosomes 46,XX for females and 46,XY for males Can point out gross chromosomal abnormalities (such as extra or missing chromosomes)

DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) Lesson Three DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid)

Components of DNA / RNA Phosphate group Sugar group Bases Deoxyribose in DNA Ribose in RNA Bases Adenine, guanine, cytosine, thymine in DNA Adenine, guanine, cytosine, uracil in RNA

The components of nucleotides The components of nucleotides. The three building blocks of a nucleotide are one or more phosphate groups, a sugar, and a base. The bases are categorized as purines (adenine and guanine) and pyrimidines (thymine, uracil, and cytosine).

The structure of nucleotides found in (a) DNA and (b) RNA The structure of nucleotides found in (a) DNA and (b) RNA. DNA contains deoxyribose as its sugar, and the bases A, T, G, and C. RNA contains ribose as its sugar, and the bases A, U, G, and C.

RNA Structure RNA is generally single stranded Can fold and create complicated structure Multiple types of RNA, each with a different function Sugar-phosphate groups form the backbone of the molecule Nucleotides are organized 5’ to 3’ Bases form the center of the molecule

5’ end A strand of RNA. This structure is very similar to a DNA strand, except that the sugar is ribose instead of deoxyribose and uracil is substituted for thymine 3’ end

Double stranded RNA: Possible secondary structures of RNA molecules Double stranded RNA: Possible secondary structures of RNA molecules. The double-stranded regions are depicted by connecting hydrogen bonds. Loops are noncomplementary regions that are not hydrogen bonded with complementary bases. Double-stranded RNA structures can form within a single RNA molecule or between two separate RNA molecules

DNA Structure DNA is a double helix Sugar-phosphate groups form the backbone Two DNA strands are anti-parallel One strand, nucleotides are organized 5’ to 3’ Other strand, nucleotides are organized 3’ to 5’ Bases are held together by hydrogen bonds and are complementary A is complementary to T C is complementary to G

A strand of DNA. This shows the phosphodiester backbone of DNA, which is a very strong bond.

3’ end 5’ end

Key features of the structure of the double helix

DNA Replication Uncoil DNA  Strand Separation   Strand Separation  Templates are Single Stranded  RNA Primers Needed For New Strands  Both DNA Strands Extended From the RNA Primer (5’ to 3’) One Strand is the Leading Strand Other Strand is the Lagging Strand

Enzymology of DNA replication – note that one strand is made continuously and is called the Leading strand, while the other strand needs to be made in pieces (called Okazaki fragments) and is called the lagging strand. One strand needs to be made in pieces because the polymerase can only work by making the new strand in the 5’ to 3’ direction (only works in one direction).