Biology 141

1. Biology 141 The Cellular Level of Organization Chapter 3: Cell Division and Protein Synthesis

2. Macromolecule Structure DNA nucleic acid • Right-handed double-helix • sugar - phosphate backbone (sides of the ladder). • nucleic acid rungs bonded by hydrogen bonds following base-pairing rules of A=T and C=G.

3. Macromolecule StructureDNA nucleic acid • DNA is wrapped on histone proteins forming nucleosomes. • Nucleosomes wind or fold into thicker structures called chromatin. • Prior to cell division • the chromatin condenses = chromosome. • One strand of DNA per chromosome. • humans = 46 chromosomes

5. DNA Replication • DNA makes an exact copy of itself prior to cell division. • The copy is attached at the centromere until cell division occurs.

7. Nucleotide sequence is the biological code. • Group of 3 nucleotides is a codon. • 1 Codon codes for 1 amino acid. • Remember – there are 20 different amino acids.

8. Macromolecule Structure RNA nucleic acid • RNA is single-stranded • (not double-stranded, can fit through nuclear pores) • Ribose sugar • (instead of deoxyribose) • Uracil • (instead of thymine) • DNA synthesizes RNA - called transcription.

9. DNA Function = Protein Synthesis • carries the blueprint for all proteins and enzymes that determine structure and function of all tissues. • Functional unit of DNA = GENE • A gene is the DNA template for a specific protein.

10. Protein Synthesis Steps: • transcription - mRNA synthesis • DNA to mRNA transcript. • DNA gene is transcribed onto an mRNA molecule. • translation - polypeptide synthesis • mRNA to amino acid sequence • mRNA is translated into protein by ribosomes and tRNA molecules.

11. Transcription DNA codes RNA molecule.Requires 3 steps: 1. Initiation: DNA unwinds. • Hydrogen bonds break. - unzips. 2. Elongation: Nucleotides are joined by RNA polymerase enzyme. • mRNA Nucleotides match up according to base pairing rules • AT • CG 3. Termination: mRNA falls off upon reaching a stop signal. DNA rewinds. • New mRNA molecule leaves nucleus.

12. transcription

13. Translation • A set of 3 nucleic acid bases on the mRNA is a codon. • A tRNA matches to the codon using base-pairing rules. • Opposite end of tRNA has one of the 20 amino acids.

14. Translation • mRNA leaves the nucleus through the nuclear pore and enters cytoplasm. • Once outside the nucleus, the mRNA is translated into protein. • Translation Requires 3 Steps: Initiation, elongation and termination.

15. Translation 1. Initiation: • Small Ribosome subunit attaches, scans mRNA for start signal. • Large ribosome subunit attaches. 2. Elongation: • Once small and large subunits bind, ribosome attracts tRNA molecules. • Begins attaching amino acids by binding tRNA molecules according to codons. Amino acids link together with peptide bonds to form a chain. • A chain of amino acids = primary structure of a polypeptide (protein). 3. Termination: • Ribosome stops at a stop codon, the tRNA stops attaching amino acids. • The ribosome subunits dissociate. • mRNA is released, new protein is released.

16. Translation

17. DNA Mutation • Mutation in a body cell DNA = cancer • Mutation in gamete (sex cell) DNA = disease or abnormality.

18. Cell Cycle (life) • Cell cycle is divided into 2 phases. • Phase 1: interphase • G1- protein synthesis, organelles replication begins • S- DNA replicates • G2 – protein synthesis, organelle replication ends

19. Cell Cycle (life) • Cell cycle is divided into 2 phases. • Phase 2: cell division. • Prophase • Metaphase • Anaphase • Telophase • cytokinesis

21. Cell Division • Somatic (body) cell division – mitosis • Replaces dead cells • New additional cells for growth • 46 (23 pair) chromosomes (diploid) • Gamete (sex) cell division – meiosis • 23 chromosomes (haploid) • Egg • sperm

22. Cell Division: Mitosis • Nuclear division: • Prophase • Metaphase • Anaphase • Telophase • Cytoplasm division • Cytokinesis

23. Prophase • Breakdown of nuclear envelope and nucleolus. • DNA condenses. • Centrioles move to opposite poles, spindle forms.

24. Metaphase • No nuclear membrane. • Chromatids separate. • Spindle attaches to individual chromatids. • Chromatids align on metaphase plate.

25. Anaphase • Chromatids pulled to the opposite poles. • Cytokinesis begins.

26. Telophase • Nuclear envelope reforms. • Nucleolus reforms. • Spindle breaks down. • Cytokinesis continues. • DNA unfolds.

27. Cytokinesis • Cytoplasm completely divides. • Animals - furrowing of cytoplasm pinches off two new cells.

28. Cell Division - Meiosis • Nuclear Division of sex cells • Meiosis - egg and sperm; Two nuclear divisions results in 4 unique haploid cells.

29. Meiosis I • Prophase I - chromosomes pair with homologous chromosomes (synapsis) to form a tetrad. • Crossing over occurs - source of genetic recombination and variation. Nucleus breaks down.

30. Prophase I

31. Prophase I

32. Prophase I

33. Metaphase I and Anaphase I • Metaphase I - tetrads align on metaphase plate. • Anaphase I - tetrads pulled apart; chromosomes pulled to opposite poles.

34. Meiosis I • Telophase I. - Cell divides into two cells. Each cell contains one chromosome from homologous pair.

35. Meiosis I • Interkinesis - short rest period between divisions. • Chromosomes still consist of sister chromatids (2 chromatids).

36. Meiosis II • Prophase II - centrioles move to opposite poles, spindle forms.

37. Meiosis II • Metaphase II - spindle attaches to centromere, chromosomes align on metaphase plate. • Anaphase II - sister chromatids separate - pulled to opposite poles.

39. Meiosis II • Telophase II. - Spindle breaks down, nuclear envelope reforms, cytokinesis continues.

40. Meiosis II • Cytokinesis - cell cytoplasm division completes. • Results in 4 new cell - each daughter cell with unique genetic haploid number of chromosomes.