Chapter 4 Genetics And. Cellular Function 4-1. Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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1 Chapter 4 Genetics And Cellular Function Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4-1

2 Genetics and Cellular Function Genes and nucleic acids Protein synthesis and secretion DNA replication and the cell cycle 4-2

3 Organization of the Chromatin Threadlike chromatin = chromosomes = 46 DNA molecules and associated proteins Nondividing state = DNA molecules compacted coiled around core particle (histone protein) zig-zagged, looped and coiled onto itself Preparing to divide DNA copies itself to form 2 parallel sister chromatids 4-3

4 DNA Structure: Twisted Ladder DNA molecule described as double helix. 4-4

5 Nucleotide Structure DNA = polymer of nucleotides Each nucleotide consist of phosphate group sugar ribose (RNA) deoxyribose (DNA) nitrogenous base in this picture = adenine 4-5

6 Nitrogenous Bases Purines - double ring guanine adenine Pyrimidines - single ring uracil - RNA only thymine - DNA only cytosine both DNA bases =CTAG RNA bases = CUAG 4-6

7 Complementary Base Pairing Nitrogenous bases united by hydrogen bonds DNA base pairings A-T and C-G Law of complementary base pairing one strand determines base sequence of other Segment of DNA 4-7

8 DNA Function Code for protein synthesis Gene - sequence of DNA nucleotides that codes for one protein Genome - all the genes of one person humans have estimated 30-35,000 genes other 98% of DNA noncoding junk or regulatory 4-8

9 RNA: Structure and Function RNA smaller than DNA (fewer bases) transfer RNA (trna) bases messenger RNA (mrna) over 10,000 bases DNA has over a billion base pairs Only one nucleotide chain (not a helix) ribose replaces deoxyribose as the sugar uracil replaces thymine as a nitrogenous base Essential function interpret DNA code direct protein synthesis in the cytoplasm 4-9

10 DNA directs the synthesis of all cell proteins including enzymes that direct the synthesis of nonproteins Different cells synthesize different proteins dependent upon differing gene activation 4-10

11 DNA Replication

12 DNA Replication 2 Law of complimentary base pairing allows building of one DNA strand based on the bases in 2 nd strand Steps of replication process DNA helicase opens short segment of helix replication fork is point of separation of 2 strands DNA polymerase assembles new strand of DNA next to one of the old strands 2 DNA polymerase enzymes at work simultaneously 4-12

13 DNA Replication 3 Semiconservative replication each new DNA molecule contains one new helix and one conserved from parent DNA Additional histones made in cytoplasm Each DNA helix winds around histones to form nucleosomes 46 chromosomes replicated in 6-8 hours by 1000 s of polymerase molecules 4-13

14 Errors and Mutations Error rates of DNA polymerase in bacteria, 3 errors per 100,000 bases copied Proofreading and error correction a small polymerase proofreads each new DNA strand and makes corrections results in only 1 error per 1,000,000,000 bases copied Mutations - changes in DNA structure due to replication errors or environmental factors some cause no effect, some kill cell, turn it cancerous or cause genetic defects in future generations 4-14

15 Protein Synthesis 4-15

16 Genetic Control of Cell Action through Protein Synthesis 4-16

17 Transcription Protein Synthesis messenger RNA (mrna) is formed from an activated gene mrna migrates to cytoplasm Translation mrna code is read by ribosomal RNA as amino acids are assembled into a protein molecule transfer RNA delivers the amino acids to the ribosome 4-17

18 Genetic Code System that enables the 4 nucleotides (A,T,G,C) to code for the 20 amino acids Base triplet: found on DNA molecule (ex. TAC) nucleotides that stand for 1 amino acid Codon: mirror-image sequence of nucleotides found in mrna (ex AUG) 64 possible codons (4 3 ) often 2-3 codons represent the same amino acid start codon = AUG 3 stop codons = UAG, UGA, UAA 4-18

19 Transcription Copying instructions from DNA to RNA RNA polymerase binds to DNA at site selected by chemical messengers from cytoplasm opens DNA helix and transcribes bases from 1 strand of DNA into pre-mrna if C on DNA, G is added to mrna if A on DNA, U is added to mrna, etc. rewinds DNA helix Pre-mRNA is unfinished nonsense (introns) removed by enzymes sense (exons) reconnected and exit nucleus 4-19

20 Alternative Splicing of mrna One gene can code for more than one protein Exons can be spliced together into a variety of different mrnas. 4-20

21 Translation of mrna mrna begins with leader sequence binding site for ribosome Start codon AUG 4-21

22 Steps in Translation of mrna Converts alphabet of nucleotides into a sequence of amino acids to create a specific protein Ribosome in cytosol or on rough ER small subunit attaches to mrna leader sequence large subunit joins and pulls mrna along as it reads it start codon (AUG) where protein synthesis begins small subunit binds activated trna with corresponding anticodon large subunit enzyme forms peptide bond 4-22

23 Steps in Translation of mrna Growth of polypeptide chain next codon read, next trna attached, amino acids joined, first trna released, process repeats and repeats Stop codon reached and process halted polypeptide released and ribosome dissociates into 2 subunits 4-23

24 Transfer RNA (trna) Activation by ATP binds specific amino acid and provides necessary energy to join amino acid to growing protein molecule Anticodon binds to complementary codon of mrna 4-24

25 Polyribosomes 4-25

26 Polyribosomes and Signal Peptides Polyribosome cluster of ribosomes reading mrna at one time horizontal filament - mrna large granules - ribosomes beadlike chains projecting out - newly formed proteins takes 20 seconds to assemble protein of 400 amino acids cell may produce > 150,000 proteins/second Signal peptide = beginning of chain of amino acids determines protein s destination within cell 4-26

27 DNA and Peptide Formation 4-27

28 Chaperones and Protein Structure Newly forming protein molecules must coil or fold into proper 2 nd and tertiary molecular structure Chaperone proteins prevent premature folding, assist in proper folding and escort protein to final destination 4-28

29 Protein Packaging and Secretion 4-29

30 Posttranslational Modification in Rough ER Proteins destined for secretion or packaging are assembled on rough ER and sent to Golgi complex Signal peptide drags new protein from ribosome through pore into cisterna of ER Posttranslational modification of protein in ER remove some amino acids, fold the protein adding disulfide bridges or adding carbohydrates Rough ER pinches off transport vesicles fuse with and empty into nearest Golgi complex 4-30

31 Posttranslational Modification in Golgi Complex Protein modified in cisterna, passed to next cisterna Last golgi cisterna releases finished product as membrane bound vesicles secretory vesicles migrate to plasma membrane and release product by exocytosis lysosomes vesicles that remain in cell 4-31

32 Cell Cycle G 1 phase, the first gap phase accumulates materials needed to replicate DNA S phase, synthesis phase DNA replication G 2 phase, second gap phase replicates centrioles synthesizes enzymes for division M phase, mitotic phase nuclear and cytoplasmic division G 0 phase, cells that have left the cycle Cell cycle duration varies between cell types 4-32

33 Mitosis one cell divides into 2 daughter cells with identical copies of DNA Functions of mitosis embryonic development tissue growth replacement of dead cells repair of injured tissues Phases of mitosis (nuclear division) prophase, metaphase, anaphase, telophase 4-33

34 Mitosis 4-34

35 Mitosis: Prophase 1 Chromatin coils into genetically identical, paired, sister chromatids each chromatid contains a DNA molecule remember: genetic material (DNA) was doubled during S phase of interphase Thus, there are 46 chromosomes with 2 chromatids/chromosome and 1 molecule DNA per chromatid. 4-35

36 Prophase 2 Nuclear envelope disintegrates Centrioles sprout microtubules that push them apart and towards each pole of the cell spindle fibers grow towards chromosomes attach to kinetochore on side of centromere spindle fibers pull chromosomes towards cell equator 4-36

37 metaphase Chromosomes line up on one equator Mitosis spindles finished spindle fibers (microtubules) attach centrioles to long centromere shorter microtubules anchor centrioles to plasma membrane (aster) 4-37

38 anaphase Enzyme splits 2 chromatids apart at centromere Daughter chromosomes move towards opposite poles of cells with centromere leading the way motor proteins in kinetochore move centromeres along spindle fibers as fibers are disassembled 4-38

39 telophase New nuclear envelopes formed by rough ER Chromatids uncoil into chromatin Mitotic spindle breaks down Nucleus forms nucleoli 4-39

40 Cytokinesis Division of cytoplasm into 2 cells overlaps telophase Myosin pulls on microfilaments of actin in the membrane skeleton creates crease around cell equator called cleavage furrow Cell pinches in two interphase has begun 4-40

41 Timing of Cell Division Cells divide when: Have enough cytoplasm for 2 daughter cells DNA replicated Adequate supply of nutrients Growth factor stimulation Open space due to neighboring cell death Cells stop dividing when: Loss of growth factors or nutrients Contact inhibition 4-41

42 Chromosomes and Heredity Heredity = transmission of genetic characteristics from parent to offspring karyotype = chart of chromosomes at metaphase 23 pairs homologous chromosomes in somatic cells (diploid number of chromosomes) 1 chromosome inherited from each parent 22 pairs called autosomes one pair of sex chromosomes (X and Y) normal female has 2 X chromosomes normal male has one X and one Y chromosome Sperm and egg contain only 23 chromosomes fertilized egg has diploid number of chromosomes 4-42

43 Karyotype of Normal Male 4-43