Cell Cycle PDF

Chapter 12 Cell Cycle Cell Division Cell division is the process by which a single cell becomes two daughter cells. oWhile this may seem simple, this process must satisfy some important requirements: 1) The two daughter cells must each receive the full complement of genetic material present in the s...

Chapter 12 Cell Cycle Cell Division Cell division is the process by which a single cell becomes two daughter cells. oWhile this may seem simple, this process must satisfy some important requirements: 1) The two daughter cells must each receive the full complement of genetic material present in the single parent cell. 2) The parent cell must be large enough to divide in two and still contribute sufficient cytoplasmic components to each daughter cell. Prokaryotic cells divide by binary fission Eukaryotic cells divide by mitosis and cytokinesis Cell Division Three events need to happen for a cell to divide: 1. Copying the DNA 2. Separating the copies 3. Dividing the cytoplasm to create two complete cells Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle Prokaryotes vs. Eukaryotes How do prokaryotes and eukaryotes differ with respect to their genetic material? Single circular strand of DNA in prokaryotes vs. linear chromosomes in eukaryotes Nucleoid vs. nucleus Binary Fission During binary fission, a prokaryote cell: 1. 2. 3. replicates its DNA Increases in size Divides into two daughter cells. oEach daughter cell receives one copy of the replicated parental DNA. Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle What is a Chromosome? In eukaryotic cells, a chromosome is a long double helix of DNA wrapped around proteins called histones. This loosely packed DNA and proteins is called chromatin. Every species has a characteristic number of chromosomes. How many chromosomes do humans have? DNA encodes the cell’s genetic information. A gene is a section of DNA that codes for a specific RNA. Therefore codes for a specific protein. Chromosomes Before mitosis, each chromosome is replicated. oEach DNA copy is called a chromatid. § At first, chromatids are attached along their entire length by proteins called cohesins. § Once mitosis begins, they are attached only at the centromere. Chromatids attached together are called sister chromatids. o Two attached sister chromatids are still considered a single chromosome. Chromosomes Proteins Involved in Mitosis Cohesins: o Form rings that hold sister chromatids together. Condensins: o Ring-shaped and condense the DNA. Nuclear lamins: o Intermediate filaments that form an interface between the chromosome and inside of the nuclear envelope. Kinetochore proteins: o Sites where microtubules connect to chromosomes. Microtubules: o Move chromosomes to the poles. Spindle Apparatus The spindle apparatus produces mechanical forces that: Move replicated chromosomes during early mitosis. Pull chromatids apart in late mitosis. The spindle apparatus is made of microtubules, formed from microtubuleorganizing centres (MTOCs). In animal cells, MTOCs are centrosomes, each containing a pair of centrioles. In plant cells, MTOCs are NEDD1 complexes. Spindle Apparatus MTOCs define the two poles of the spindle apparatus. Plus ends of microtubules grow outward from each pole. Polar microtubules extend from each spindle pole and overlap with each other. Astral microtubules anchor spindle poles in place. Microtubules that attach to chromosomes are called kinetochore microtubules. MTOCs Kinetochore Microtubule Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle Cell Cycle (Eukaryotes) Cell division in eukaryotes proceeds through a number of steps that make up the cell cycle. The cell cycle consists of two distinct stages: 1) M phase: the time during which the parent cell divides into two daughter cells. 2) Interphase: the time between two successive M phases. Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle Interphase Cells spend most of their time in interphase. Chromosomes are uncoiled. Cells are growing and preparing for division or are fulfilling their specialized functions. Three phases in interphase: G1 or the first gap phase § Cell growth and protein content increase. § Many regulatory proteins are activated S phase § Synthesis phase § DNA replication G2 or the second gap phase § Cell prepares for mitosis and cytokinesis Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle M Phase M phase consists of two distinct events: 1. Mitosis: the division of the replicated chromosomes. 2. Cytokinesis: the division of the cytoplasm. M Phase Mitosis Stages 1 2 3 4 5 Prophase Prometaphase metaphase Anaphase Telophase Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle Cytokinesis (Animal) As mitosis ends, cytokinesis begins, and the parent cell divides into two daughter cells. oIn animal cells, this stage begins when a ring of actin filaments, called the contractile ring, forms. § This ring contracts, pinching the cytoplasm of the cell forming a cleavage furrow and dividing in in two. Cytokinesis (Plant) Since plant cells have a cell wall, the division of the cell is achieved by constructing a new cell wall. oVesicles from the Golgi apparatus bring membrane and cell wall components to the middle of the cell forming a cell plate. § Once the cell plate is large enough, it fuses with the original cell wall at the perimeter of the cell and cytokinesis is complete. Lecture Outline 1. Binary Fission in Prokaryotes 2. Cell Division in Eukaryotes a) Vocabulary b) Cell Cycle i. Interphase ii. Mitosis iii. Cytokinesis c) Control of the Cell Cycle Control of the Cell Cycle Cell-cycle length can vary greatly among cell types, mostly due to variation in the length of G1 phase. oRapidly dividing cells essentially eliminate G1 phase. oNondividing cells get permanently stuck in G1 phase. § This arrested state is called the G0 state. Division rate can also vary in response to changing conditions. Cell-Cycle Checkpoints There are four cell-cycle checkpoints: G1 checkpoint G2 checkpoint M-Phase checkpoints Cells that divide without control may form a tumour. Cancer Cancerous cells have two types of defects: Defects that activate the proteins required for cell growth when they should not be active. Defects that prevent tumour suppressor genes from shutting down the cell cycle. Two types of tumours: Benign tumours are noncancerous and noninvasive. Malignant tumours are cancerous and invasive. Can spread throughout the body via the blood or lymph and initiate secondary tumours. This process is called metastasis.