Cell Biology Unit Seven

The Cytoskeleton The cytoskeleton is a series of tubules and filaments that have a variety of functions: ~ determine cell shape ~ organelle attachment ~ provide cell movement ~ provide organelle movement ~ spindle formation

The Cytoskeleton The tubules and filaments of the cytoskeleton are comprised of protein and are divided into three categories: ~ microtubules ~ microfilaments ~ intermediate filaments

The Cytoskeleton Microtubules are hollow tubes that are the largest of the three components In cross section they appear as thirteen subunits (protofilaments) made of globular protein units called tubulin

The Cytoskeleton

The Cytoskeleton Microtubules are the major component of the cytoskeleton, centrioles, flagella & cilia

The Cytoskeleton Microfilaments are solid protein polymers found in muscle cells There are thin microfilaments (actin) and thick microfilaments (myosin) These microfilaments produce muscle cell contractions

The Cytoskeleton

The Cytoskeleton Intermediate filaments are solid protein polymers found in several different forms They comprise part of the cytoskeleton and aid in the positioning of organelles

The Cytoskeleton Intermediate filaments confer most of the mechanical strength of the cytoskeleton

Flagella and Cilia Microtubules form the skeleton of flagella and cilia The pattern is a 9+2 arrangement of microtubules that is covered with the cell membrane There are nine pair of microtubules that surround two singles

Flagella and Cilia The paired microtubules have ATPase attached which provides the energy needed for movement The movement is thought to be created by sliding

Flagella and Cilia

Centrioles Centrioles are bundles of microtubules that are arranged in nine triplet sets In animals there are two per cell, set perpendicular to each other Centrioles form the centrosome which produce microtubules for use in the cell

Centrioles Centrioles separate during cell division producing the spindle (spindle fibers) Cilia & flagella grow from centrioles that have migrated to the plasma membrane Two of each of the triplet sets will begin to grow, forming the pairs of microtubules in these strucuture

Centrioles

DNA Replication DNA replication occurs during the S phase of interphase in preparation for cell division It is semi-conservative, meaning each strand of the original acts as a template for a new strand

DNA Replication DNA replication occurs in two stages: + synthesis of nucleotides + synthesis of new DNA strands

DNA Replication DNA nucleotides are synthesized in the cytoplasm They are first synthesized with ribose, then converted to deoxyribose They are then transported into the nucleus for DNA replication

DNA Replication DNA replication occurs in the nucleus under the direction of several enzymes Synthesis always occurs in the 5’→3’ direction with the addition of nucleotides on the 3’ end

DNA Replication

DNA Replication

DNA Replication

The Characteristics and Functions of Cell Division (Mitosis) Begins with a diploid cell & ends identical diploid cells Occurs for growth, repair & replacement

The Characteristics and Function of Meiosis Production of gametes Begins with a diploid sex cell & ends with non-identical haploid gametes Assures correct chromosome numbers in offspring

Interphase G1 – organelles double S – DNA replicates G2 – proteins produced

Mitosis Prophase Metaphase Anaphase Telophase

Plant Mitosis

Cytokinesis

Significance of Cell Division Cell division (mitosis) is an efficient process that assures the correct number of chromosomes will be found in the new daughter cells

Significance of Cell Division Chromosome number is a critical characteristic in determining a species and the viability of an organism Correct chromosomes numbers are essential for successful fertilization events

Significance of Cell Division In animals, increasing or decreasing chromosome numbers has deleterious effects In plants, the increase in the number of chromosomes can lead to polyploidy

Significance of Cell Division Cellular homeostasis is maintained by a number of factors: + cell size + nutrient availability + DNA damage + growth factors + cell population density

Significance of Cell Division

Significance of Cell Division Surface to volume ratio determines the maximum size a cell can obtain The amount of nutrients available is a factor in the rate of growth Growth factors such as cyclins, Cdks and hormones influence the speed and amount of cell growth

Significance of Cell Division The density of cells also controls cell growth – loss of cells stimulates cell division, adequate numbers of cells inhibit the process

Cancer Cell division is orchestrated by proteins and hormones so that growth and division is controlled Cancer cells are normal body cells that are transformed. In this transformed state, they ignore the controls of cell division and multiply unchecked

Cancer Normally, the immune system destroys these cancer cells, but some may escape destruction and then form a tumor A tumor is a mass of cancer cells found within otherwise normal tissue

Cancer A tumor is said to be benign if the cancer cells remain within the tumor. These can usually be removed through surgery A malignant tumor contains cancer cells that are invasive, meaning they spread to other tissues. A person with a malignant tumor is said to have cancer

Cancer Remember - cell division is orchestrated by proteins and hormones so that growth and division is controlled Oncogenes are those that initiate cell division, but in an accelerated and exaggerated process

Cancer Tumor suppressor genes are those that prevent cell division and promote normal cell death If tumor suppressor genes are altered, inactivated or removed the result can be cancer

Cancer Cancer can occur through genetic abnormalities, activating oncogenes and/or inactivating tumor suppressor genes Environmental influences can also affect the activity and inactivity of these genes

Cancer Environmental influences include: ~ diet ~ exercise ~ sun exposure ~ smoking ~ altering of DNA

Meiosis Meiosis is the cell division process by which gametes are produced It occurs only in sex cells that are found in the gonads

Meiosis The process goes through two meiotic divisions – meiosis I and meiosis II

Meiosis Homologous chromosomes

Meiosis

Meiosis

Meiosis

Meiosis vs. Mitosis

Spermatogenesis

Oogenesis