Chromosomes and Cell Reproduction Chapter 6 and Section 9.1 in Green Book Chromosomes and Cell Reproduction

Essential Vocabulary Text Book: Green Book: Somatic cells Cell cycle Gamete Autosome Binary fission Sex chromosome Gene Chromosome Karyotype Chromatid Cell cycle Centromere Interphase Homologous chromosome Mitosis Cytokinesis Diploid Cancer Haploid spindle Zygote Green Book: Somatic cells Cell cycle Interphase Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis Replicate Centromere chromatin

Chromosomes Section 6.1 Key Concepts Cell division allows organisms to reproduce asexually, grow, replace worn-out or damaged tissues, and form gametes. Bacteria reproduce by binary fission. Before cell division, DNA coils tightly around proteins and forms chromosomes. At cell division, each chromosome consists of two chromatids attached at the centromere. Each organism has a characteristic number of chromosomes. Human somatic cells are diploid, with 23 pairs of homologous chromosomes. Human gametes are haploid with 23 chromosomes. Sex chromosomes carry information that determines an organism’s sex. Changes in chromosome number or structure can cause abnormal development. Karyotypes are used to examine an individual’s chromosomes.

Objectives Identify four examples of cell division in eukaryotes and one example in prokaryotes Differentiate between a gene, DNA molecule, chromosome, and chromatid Compare haploid and diploid cells Predict how changes in chromosome number or structure can affect development

How Cells are Formed by Cell Division Regardless of the type of division, DNA must be present in the resulting cells. When a cell divides, the DNA is first copied and then distributed so that each cell ends up with a complete set of the DNA. About 2 trillion cells are produced by an adult human body every day! Cell division occurs in humans and other organisms at different times in their life. Bacterial cells undergo reproduction by dividing Eukaryotic cells undergoing growth, development, repair, or sexual reproduction divide by a different type of cell division. The formation of reproductive cells, called gametes, is yet a third type.

Bacterial cells divide to reproduce Bacterium’s single DNA molecule is circular and is attached to the inner cell membrane. Bacteria reproduce by a type of cell division called binary fission. Binary fission is a form of asexual reproduction that produces identical offspring.

Binary Fission Occurs in 2 stages DNA is copied The cell divides Divides by adding a new cell membrane to the point on the membrane between the two DNA copies New cell wall forms around the new membrane Eventually pinched into 2 independent but identical cells

Eukaryotic cells form chromosomes before cell division Vast amount of information encoded in DNA is organized into units call genes A gene is a segment of DNA that codes for a protein or RNA molecule Linked like a train Genes play an important role in how a person develops and functions DNA is stretched out so information can be used to direct protein synthesis

Chromosomes: coiling and division As a eukaryotic cell prepares to divide, the DNA and the proteins associated with the DNA coil into a structure called a chromosome. Before it coils, DNA is copied Two exact copies make up a chromatid and attached at centromere Centromere is the point of separation during cell division

Chromosome Number and Structure Affect Development Each human somatic cell (any cell that isn’t a gamete) normally has 23 pairs of chromosomes They differ in size, shape, and set of genes Each chromosome contains thousands of genes that play important roles in determining how a person’s body develops and functions. For this reason, possession of all chromosomes is essential to survival.

Sets of chromosomes Homologous chromosomes are chromosomes that are similar in size, shape, and genetic content Each one in a set comes from one parent 1 from mom, 1 from dad

Sets of chromosomes Diploid- contains two sets of chromosomes Somatic cells 2n Haploid- contains one set of chromosomes Gametes n Zygote- fertilized egg cell, first cell of new individual

Each organism has a characteristic number of chromosomes

Chromosomes determine your sex Autosomes are chromosomes that are not directly involved in determining gender Sex chromosomes determine gender

Change in chromosome number

Change in chromosome structure Changes in an organism’s chromosome structure are called mutations Deletion- a piece of chromosome breaks off completely Duplication- chromosome fragment attaches to its homolog Inversion- chromosome piece reattaches to the original chromosome backwards Translocation- piece reattaches to a nonhomologous chromosome

Section 6.1 Review Summarize how bacterial cells divide by binary fission. Identify the point in a eukaryotic cell’s life at which DNA coils up to form chromosomes. Summarize the difference between a haploid cell and a diploid cell. Compare the sex chromosomes of human females with those of human males. Compare the karyotype of an individual with Down syndrome with a normal karyotype. A student concludes that homologous chromosomes are found in gametes. Do you agree or disagree?

The Cell Cycle Key Concepts Section 6.2 Key Concepts The life of a eukaryotic cell—the cell cycle– includes interphase, mitosis, and cytokinesis. Interphase consists of 3 phases: growth, DNA synthesis (replication), and preparation for cell division. A cell about to divide enters the mitosis and cytokinesis phases of the cell life cycle. The cell cycle is carefully controlled; failure of cellular control can result in cancer.

Objectives Identify the major events that characterize each of the five phases of the cell cycle Describe how the cell cycle is controlled in eukaryotic cells Relate the role of the cell cycle to the onset of cancer

The Cell Cycle Describes the Life of a Eukaryotic Cell The life of a eukaryotic cell is traditionally shown as a cycle The cell cycle is a repeating sequence of cellular growth and division during the life of an organism A cell spends 90% in interphase, the first phase Only moves forward to the next phases when it is about to divide Cell division in eukaryotic cells is more complex than cell division in bacteria Organelles have to be rearranged before the cell can properly divide and form 2 fully functioning cells

The cell cycle First Growth (G1) phase- the cell grows rapidly and carries out routine functions Synthesis (S) phase- DNA is replicated, two chromatids attached at centromere Second Growth (G2) phase- preparations are made for nucleus to divide, microtubules are assembled Mitosis- the process of cell division in which the nucleus of the cell is divided into two nuclei Cytokinesis-the process during cell division in which the cytoplasm is divided

The cell cycle

The Cell Cycle is Carefully Controlled If a cell spends 90% of its time in interphase, how do cells know when to divide? How is the cell cycle controlled? Like traffic lights, cells have a set of “red light—green light” switches that are regulated by feedback information from the cell. The cell cycle in eukaryotes is controlled by many proteins. Control occurs in three principal checkpoints.

Checkpoints Cell Growth (G1) Checkpoint-makes the key division if the cell will divide. Cell must be healthy and large enough. Cell will hit a yellow light if it needs a resting period DNA Synthesis (G2) Checkpoint- DNA replication is checked at this point by DNA repair enzymes Mitosis Checkpoint- triggers the exit from mitosis, signals beginning of G1 phase

Section 6.2 Review Differentiate between the G1, G2, and S phases of the eukaryotic cell cycle. Relate the onset of cancer to three major check-points at which the cell cycle is controlled. Identify the type of environmental factors that can cause mutations that may lead to cancer. Why are individual chromosomes more difficult to see during interphase than during mitosis?