bio- cell cycle

ANAPHASE 1

homologous pairs of chromosomes are pulled toward opposite poles Spindle fibers shorten to pull the chromosomes

Prophase 1

centrioles divide and migrate to opposite poles of the cell, spindle fibers form, chromosomes appear, homologous chromosomes form tetrads (4) and crossing over occurs

TELOPHASE 1 and CYTOKINESIS

nuclear membrane may re-form (unless going directly into meiosis 2 Cell divides At the end of meiosis 1 the cells have the haploid number of chromosomes but the chromosomes are still made up of sister chromatids

DIFFERENT STEM CELLS

A fertilized egg is known as a totipotent- it can literally become any type of cell Embryonic stem cells are pluripotent and came form most types of cells Adult stem cells are multipotent and are more limited in the types of cells that they can become

ETHICAL CONCERNS

Because adult stem cells can be harvested from a willing, living donor there tends to be little concern about the use of these cells (remember- they are as flexible) Because the harvesting of embryonic stem cells often requires the destruction of an embryo they raise ethical concerns for some people Being able to harvest embryonic stem cells without harming the embryo or finding a way to get adult stem cells to act like embryonic stem cells would take care of many of these concerns

PROPHASE

Begins the active process of mitosis, the following events occur: Chromosomes supercoil and appear Nuclear membrane (envelope) breaks down Centrioles divide and they begin migrating toward poles Early stages of spindle fiber development

DIFFERENTIATION IN C. ELEGANS

Caenorhabditis elegans is a small nematode, or a roundworm, has been extensively studied Its development has been carefully mapped out and it is remarkably consistent By studying these we can better understand how differentiation works They are known as a model organism which is an organism used in a particular field of biology that can be used to explain other more complex organisms

THE CELL CYCLE

Can be thought of as the life cycle of a cell The cell cycle is divided in a number of ways The mitotic phase is that time when the nucleus and cell are actually dividing Interphase refers to the events that occur between mitotic divisions, a variety of events are occurring during this time At the end of mitosis (beginning of interphase) each chromosome is made up of a single chromatid The events of interphase prepare the cell for the next mitotic division

METAPHASE 1

Chromosomes line up IN PAIRS along the metaphase plate Spindle fibers begin attaching to centromeres

CHROMOSOME STRUCTURE

Chromosomes will occur in both duplicated and non-duplicated forms In duplicated form the chromosomes will be made up of two identical sister chromatids (left and right sides if you split the chromosome right down the middle- they are exactly the same with the exact same DNA) that are connected by a structure called a centromere In the non-duplicated form they will be made up of a single chromatid Chromosomes are made up of chromatin which is long strands of DNA wrapped around proteins called histones

DIFFERENTIATION IN MAMMALS

Differentiation in mammals is much more complex and is also more flexible The undifferentiated cells from which specialized cells develop are called stem cells Stem cells have the ability to become almost any type of cell

KEY TERMS

Diploid number- the number of chromosomes in normal body cells Haploid (or monoploid) number- ½ of the diploid number, the number of chromosomes found in a reproductive cell Somatic cell- body cells having the diploid number of chromosomes Gamete- reproductive cells having the haploid number of chromosomes

HOMOLOGOUS CHROMOSOMES

Diploid numbers are always even Chromosomes occur in homologous pairs The 2 chromosomes in a homologous pair contain genes for all the same traits, but not necessarily the same forms of the gene, the chromosomes are not identical In each pair, one came from the father (sperm) and one came from the mother (ovum or egg)

ANAPHASE

During anaphase the following events occur: Each chromosome is pulled apart at the centromere, separating the sister chromatids spindle begins pulling the sister chromatids (now separate chromosomes) toward opposite poles of the cell

METAPHASE

During metaphase the following events occur: Chromosomes line up along the equatorial plate (middle of the cell) aka metaphase plate spindle fibers grow from the centriole and attach to the chromosomes at the centromere

CROSSING OVER

During prophase 1 homologous pairs overlap and can trade pieces of chromosome This allows new combinations of genetic material

MAINTAINING CHROMOSOME NUMBER

Each species has a distinctive number of chromosomes called a diploid number This is the number of chromosomes found in a normal somatic (body) cell of that organism (any cell other than reproductive cells) When sexual reproduction occurs, 2 cells unite through fertilization If 2 somatic cells unite, they would result in a cell with twice the normal number of chromosomes Ex for humans: 46+46= 92 This won't work! Reproductive cells or gametes must have only half the normal number of chromosomes Ex for humans: 23+23=46 We're back to the correct number of chromosomes! Which 23 get passed on?- for each pair of chromosomes you get one your mother and one from your father

FERTILIZATION

Fertilization: the union of a sperm and an ovum Results in a fertilized zygote that has the diploid number of chromosomes

TELOPHASE

In telophase the following events occur: The nuclear membranes reform Chromosomes begin uncoiling spindle fibers break down Cytokinesis usually begins

APOPTOSIS

Is a process of programmed cell death This allows that cell to die in a controlled manner so that their remains do not damage neighboring cells Regulated apoptosis during development can lead to the development of complex structures, differences in apoptosis can determine the difference between the foot of a mouse and the foot of a duck

INTERPHASE

Is divided into 3 parts G1 (growth/gap 1)- the cell grows in size and differentiates into a specific cell type (after the cell divides it needs to grow back into its former size) (epithelial cells differentiate very quickly since they shed a lot, neurons never leave G1 because nerve cells don't regenerate or divide) S (synthesis, synthesizing DNA)- the DNA is copied, creating cells made up of 2 sister chromatids (takes up a lot of energy) G2 (growth 2)- the cell prepares for mitosis by checking the accuracy of the DNA, making necessary proteins, and performing other tasks (cell makes sure it has everything for the next round of division to occur) Side note: Neurons are the most complicated cells in the human body, epithelial cells are skin cells (most frequent)

MEIOSIS

Is simply the process that forms gametes by separating each homologous pair of chromosomes A gamete will end up with 1 chromosome from each pair Fertilization will result in homologous pairs again Meiosis and fertilization are kind of counterbalancing processes Meiosis will occur only in cells that are producing gametes These tissues are the ovaries in females and testes in males in animals

CYTOKINESIS

Is the division of the cytoplasm and its contents In animal cells the cell membrane simply pinches inward until the cell separates into 2 In plant cells a cell plate forms between the 2 ends of the cell and develops into a new cell wall

CANCER

Is the uncontrolled division of cells leading to the production of defective cells forming a mass of cells called a malignant tumor Benign tumors are also abnormal masses of cells but they don't invade healthy tissue When a tumor metastasis cells spread through the body, introducing cancer to new tissues of the body

DIFFERENTIATION

Is when a new cell specializes into a specific cell type (nerve, muscle, bone, blood, ect) Differentiation occurs during G1 of the cell cycle It varies between simple and complex organisms

GAMETES

Ovum: an egg cell or female gamete Sperm: a male gamete, often having flagella that make them motile

BENEFITS OF STEM CELL RESEARCH

Stem cells show great promise for repairing damaged heart tissue, treating strokes, spinal cord injuries, and treating various diseases Scientists have been able to get stem cells to develop into specialized cells on demand, even neurons There are many potential medical benefits

CONTROL OF THE CELL CYCLE

The cell cycle is controlled by 2 sets of molecules The cyclins are a group of proteins that regulate the cell cycle and determine how often a cell with go through mitosis Specific enzymes attach to the the cyclins and become activated causing a particular event of the cell cycle to occur Internal regulators respond to internal signals like whether or not the chromosomes have finished replicating External regulators respond to factors outside the cell such as causing cell division to stop when new cells come in contact with neighboring cells

MITOSIS

The word mitosis refers to the division of the nucleus and its contents The key to mitosis is ensuring that each nucleus produced gets a complete copy of the genetic material (one of each chromosome) At the beginning of mitosis chromosomes are in their duplicated form, at the end of mitosis chromosomes are in their unduplicated form Mitosis, while continuous, fluid process is divided into 4 stages, prophase, metaphase, anaphase, and telophase It copies the same cells over and over and over (copying machine) so we can grow

WHAT IS A CHROMOSOME?

They are structures found in the nucleus of the cell that is preparing to undergo nuclear division They are collections of a portion of a cell's DNA (genetic code/information) packed into a form that can be easily transported The appearance of a chromosome may change slightly depending on when during the cell cycle they are being viewed -chrome is colored -some means body meaning colored body DNA can get wrapped around proteins called histones which get twisted together and they fold back and forth and pack up even more, which makes the long thin strand into a short thick strand of DNA