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Cellular Reproduction Asexual vs. sexual reproduction • Making the next generation • Asexual – One parent – Offspring are genetically identical to parent • Sexual – Two parents – Offspring contain genes from both parents and are genetically unique Fig. 8-1a Prokaryotic asexual reproduction BINARY FISSION • Prokaryotes have a single circular chromosome • Chromosome replicates • Cell adds new membrane and cell wall between the chromosomes– cell elongates • Cell splits between two chromosomes Fig. 8-3b Prokaryotic chromosomes Fig. 8-5 CELL CYCLE IN EUKARYOTIC CELLS INTERPHASE G1 First gap phase -growth -normal cell activities S (DNA synthesis) -DNA copies (replicates) itself G2 Second gap phase -growth -cell prepares for mitosis Mitosis = division of the nucleus Cytokinesis = division of the cytoplasm Fig. 8-4bc What happens to a chromosome during the cell cycle Sister chromatids Single, replicated chromosome (G1) Chromosome is replicated/ sister chromatids (identical copies) attached at centromere Centromere Sister chromatids Replicated chromosome splits, each chromatid going to a separate cell What’s wrong with this???? Fig. 8-9a G1 checkpoint Cells can’t get past unless they get a signal from outside G0 G0 is a nondividing state Ex: brain, muscle Control system G1 M S G2 G2 checkpoint size and DNA checked M checkpoint in metaphase all c’somes attached to spindle Fig. 8-9b Growth factor -outside “signal” that it’s time to divide. -gets a cell to move past the G1 checkpoint Plasma membrane Receptor protein Relay proteins G1 checkpoint Control system G1 M G2 S Fig. 8-12 Your chromosomes are organized into homologous pairs One from mom One from dad Have genes for the same traits May be different forms of the gene however Homologous pair of chromosomes Centromere Sister chromatids One duplicated chromosome Life cycle of humans Haploid gametes (n = 23) Adults produce gametes (sex cells) by meiosis -these are haploid cells n n Meiosis Haploid gametes fuse during fertilization -forming a zygote that is diploid Zygote divides by mitosis, cells differentiate during development creating the adult Egg cell Sperm cell Fertilization Diploid zygote (2n = 46) 2n Multicellular diploid adults (2n = 46) Mitosis and development In Meiosis I, duplicated homologous chromosomes pair up and then are separated into separate cells Diploid Haploid In Meiosis II, duplicated chromosomes are split, each chromatid going into a separate cell Haploid Stages of Mitosis • Before mitosis can occur what has to happen to the chromosomes Cancer • Cells that undergo uncontrolled cell division • Invade surrounding tissue • Move by way of circulatory or lymphatic system to new location – Metastisis – Benign vs. malignant DNA Polymerase • Adds nucleotides to a growing nucleic acid chain • Can ONLY add to the 3’ end of the chain –Result: –The two sides of the DNA molecule are copied differently Role of ligase