* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
The Plant Cell Cycle Chapter 3 • Nucleus • DNA • Replication • Cytoskeleton The plant cell Cell wall CHLOROPLAST CHLOROPLAST MITOCHONDRIUM NUCLEUS MITOCHONDRIUM MITOCHONDRIUM CYTOSOL CHLOROPLAST CHLOROPLAST MITOCHONDRIUM Notes: 1) cytosol is the same as cytoplasm 2) not all of the plant cell structures and organelles are shown Plasma membrane one pore Nucleus -Ovoid or irregular shaped -Surrounded by double membrane (nuclear envelope) nuclear envelope 1 µm 0.2 µm lipid bilayer facing the nucleoplasm lipid bilayer facing nuclear the cytoplasm envelope pore complex that spans both bilayers Fig. 3-8, p. 37 Structure of Phospholipids and Glycolipids • Hydrophilic • Hydrophobic Structure of Phospholipids and Glycolipids Central dogma of Molecular Biology DNA TRANSCRIPTION REPLICATION RNA TRANSLATION Ribosome mRNA protein + Nucleolus: production center for ribosomes nuclear envelope Nucleolus (rDNA, rRNA, ribosomal proteins, etc…) Chromosome Early Prophase cell Structure of DNA A nucleosome consists of part of a DNA molecule looped twice around a core of histones (chromosomal proteins). core of histone molecules Fig. 3-9a, p. 37 Immerse a chromosome in saltwater and it loosens up to a beads-on-a-string organization. The “string” is one DNA molecule. Each “bead” is a nucleosome. Fig. 3-9b, p. 37 At a deeper level of structural organization, the chromosomal proteins and DNA are organized as a cylindrical fiber (again a helical structure). Fig. 3-9c, p. 37 Fig. 3-9d, p. 37 At times when a chromosome is most condensed (during Mitosis), the chromosomal proteins interact, which packages loops of already coiled DNA into a “supercoiled” array (two additional helical organizations). Such a tightly packaged DNA molecule is more easily moved around compared to when it would be a long “loose” thread (important during cell division) old new new old Fig. 2-18, p. 26 Cytoskeleton • Structures in cytoskeleton – Microtubules – Motor proteins – Microfilaments • Specialized proteins connect microtubules and microfilaments to other organelles – Connections thought to coordinate many cell processes Cell Cycle some cells leave the cycle pre-DNA synthetic phase or gap phase G1 cytokinesis telophase CELL DNA Interphase synthesis phase S anaphase metaphase prophase some cells leave the cycle Mitosis (M) CYCLE G2 premitosis phase Note: Interphase includes G1, S and G2 phases Fig. 3-15, p. 43 Principal Control Point Hypothesis control point G1 M S control point G2 Fig. 3-16, p. 44 A B microtubules nucleus C band of microtubules cell wall cytoplasm Fig. 3-18, p. 45 Formation of the preprophase band of microtubules in meristematic cells: A) Section at right angles to the plane of the future cell plate shows a cross section of microtubules. B) Section in the plane of the future cell plate shows microtubules encircling the nucleus. C) Three-dimensional drawing of A and B. Mitosis • Four phases – Prophase – Metaphase – Anaphase – Telophase Mitosis a d c b e cell plate nuclear envelope nucleolus pole spindle fiber chromosome kinetochore Early Prophase Late Prophase Metaphase Late anaphase Telophase Fig. 3-19, p. 46 The roles of microtubules in mitosis Fig. 3-17, p. 45 Visualization of tubulin (component of microtubules) during mitosis. Cell division in Plants versus Animals • Animal cells do not have a cell wall Because plant cells have cell walls, the direction of cell division is a major determinant of overall plant development (cells are caught in a rigid structure and cannot reorganize after cell division has been completed). The direction/orientation of cell division is controlled by plant hormones. Cell division in Plants versus Animals • Animal cells do not form a preprophase band (PPB) • During Telophase: - in plants: a cell plate is formed at the start of cytokinesis (direction of cell plate formation depends on hormone action via effects on PPB formation) - in animals: the cell pinches in the middle to form two cells, no cell plate is formed.