Chromosomes and Cell Reproduction Cell Growth Most living

Chromosomes and Cell Reproduction

Cell Growth – Most living cells are between 2 and 20 µm in diameter. • B. Once cells reach a certain size, they must stop growing or divide. However, some cells do not normally divide: 1. Nerve cells 2. Cardiac muscle cells. 3. Mature red blood cells (RBCs). – How big a cell can grow is determined by physical factors below: 1. Diffusion rate of materials into and out of the cell. (Remember diffusion only works will over short distance 2. The amount of DNA available to program the cell’s metabolism. 3. The cell’s surface area-to-volume ratio. – So, mitosis is important for cell survival by taking a large cell and dividing it into two identical smaller cells with identical diploid (2 n) genetic material.

Cell Division – Cell division, also called cell reproduction occurs in humans. 1. Eukaryotic organisms undergoing growth, development, and repair divide their cells by mitosis. 2. Bacteria cells undergoing reproduction divide by binary fission. – Binary fission is a form of asexual reproduction that produces identical offspring. – In asexual reproduction, a single parent passes exact copies of all its DNA to its offspring (clones). 3. The formation of gametes involves a third type of cell division. – Gametes, an organism’s reproductive cells, such as sperm or egg cells. – Regardless of the type of cell division that occurs, all of the DNA (deoxyribonucleic acid) must be present in each of the resulting cells.

Chromosomes: The cell structure in the nucleus that carries the genetic material—DNA. – Chromosomes are the structures that carry MOST genetic information. A. Chromosome Structure: A chromosome is a very long DNA molecule that contains many genes. Chromatin- It is the DNA and proteins in the nucleus of a nondividing cell. During most of a cell’s life cycle (interphase) chromosomes exist as chromatin, which are strands of DNA wrapped around protein molecules (uncoiled like tangled-up spaghetti). Chromatin is not visible during this stage. DNA can not be seen under a compound light microscope. DNA can be seen under an electron microscope. Chromatin Chromosome

State Test Question • What structures carry the MOST genetic information for a leaf cell? a) b) c) d) Chromosomes Ribosomes Centrioles Chloroplasts

State Test Question • Which of the structures labeled below contains chromosomes? – – a b c d

Chromosome Structure Cont. Two Parts of the Chromosome: 1. Chromatid- Before the DNA coils up, DNA is copied The chromatin coils up into two identical parts of a chromosome, which are called chromatids. AKA—sister chromatids. 2. Centromere-The point at which each pair of chromatids are attached. Holds chromatid (duplicated chromosomes) together. A chromatid is attached to a spindle fiber by the centromere.

State Test Question a) Chromatin b) Centromere c) Centriole d) Centrosome

Chromosome Numbers: 1. All sexually reproducing organisms have pairs of chromosomes. ** Organisms range in number of chromosomes from 2 to over 300. Ferns have 1, 262 Chromosomes. 2. Homologous Chromosomes: are pairs (2) of chromosomes that are similar in size, shape, and genetic content -Each homologous chromosome comes from one of the two parents. -Example: The 46 chromosomes in human somatic cells (body cells) are actually 2 sets of 23 chromosomes— 1 set from the mother -1 set from the father. -Example: If one chromosome in a pair contains a gene for eye color, so will the other chromosome in that pair.

Chromosome Numbers: 3. Diploid (2 n): When a cell, such a somatic cell, contains sets of chromosomes, it is said to be diploid. The diploid number in a somatic cell can be written as 2 n=46. **Biologists us the symbol 2 n to represent 2 sets of chromosomes. How many homologous pairs of chromosomes do humans have? __23___ 4. Haploid (n): When a cell, such as a sex cell (gamete), contains one set of chromosomes, it is said to be haploid. n= 1 set of chromosomes The haploid number in a gamete=23 n = 23 (half of 46)

Fertilization is the joining of gametes (sex cells_ from opposite sexes. A zygote is a fertilized egg cell, the first cell of a new individual. Fertilization Zygote

Chromosomes Determine Your Sex: • Of the 23 pairs of chromosomes in human somatic cells, 22 pairs are called autosomes. • Autosomes are chromosomes that are not directly involved in determining the sex (gender) of an individual. • The sex chromosomes, one of the 23 pairs of chromosomes in humans, contain genes that determine the sex of an individual. • In humans, the two sex chromosomes are X and Y chromosomes. • XY chromosomes = male • XX chromosomes = female • Because a female can donate only an X chromosome to her offspring, the sex of an offspring is determined by the male, who can donate either an X or a Y.

Change in Chromosome Structure • A change in an organism’s structure is called a mutation. • Breakage of a chromosome can lead to four types of mutations. Four Types of Mutations: 1. Deletion mutation- a piece of chromosome breaks off completely. After cell division, the new cell will lack a certain set of genes. Often this is fatal to the zygote. 2. Duplication mutation- a chromosome fragment attaches to its homologous chromosome, which then carry two copies of a certain set of genes.

Duplication Mutation Deletion Mutation

3. Inverse mutation- the chromosome piece reattaches to the original chromosome but in a reverse position. 4. If the piece of chromosome that broke off reattaches to a non-homologous chromosome, a translocation mutation Inverse Mutation results. Translocation Mutation

The Cell Cycle – – – The life of a eukaryotic cell is the cell cycle which includes interphase, mitosis, and cytokinesis. A cell can only grow so large, when it reaches a certain point it will divide into two cells. So, the cell is as large as it can get—then it divides and the two cells are small. This process is called mitosis. The cell cycle is a repeating sequence of cellular growth and division during the life of an organism. A cell spends 90% of its time in the first three phases of the cycle. What phase does the cell spend the most time? Interphase

State Test Question a) b) c) d) When using a light microscope, which of the following structures is first visible when a cell is dividing? Mitochondrion Ribosome Chromosome Lysosome

State Test Question The ongoing process in which cells grow, develop, and reproduce is called— a) meiosis. b) mitosis. c) the cell cycle. d) interkinesis.

Interphase: • The busiest and longest part of the cell cycle. • The cell is growing and the chromosomes are replicating (copying). • Before mitosis begins, the chromosomes are copied. • Each chromosome now consists of two chromatids. • *Humans have 46 chromosomes (23 pairs), so now 92 chromosomes are ready for cell division. – • 46 will end up in 1 cell, and the other 46 will end up in the 2 nd cell. DNA is the form of chromatin. – Since DNA is the form of chromatin, it is not visible

e. Interphase has 3 distinct phases: i. The G 1 (gap 1) phase: -Cellular Growth -Organelles begin to double in number. -lasts 8 -10 hours ii. S phase (synthesis) -Cellular growth -DNA synthesis—DNA (chromatin) is replicated. -Lasts about 6 -8 hours. iii. The G 2 (gap 2) phase -Cellular growth -Preparation for cell division mitosis. -Synthesis of proteins occurs. -lasts 4 -6 hours

State Test Question G 1 Phase, S Phase, and G 2 Phase are all parts of— a) Interphase. b) Anaphase. c) Prophase. d) Teophase.

Mitosis • Lasts about 1 -2 hours. • Mitosis occupies approximately 5% of the total cell cycle. • • Mitosis is the division of all somatic (body cells/non-sex cells). A cut on your hand will repair itself using the process of mitosis. The first step of mitosis is the chromatin coiling up into chromosomes. The first three steps are all involved with the splitting of the nucleus. The last step involves the splitting of the cytoplasm, known as cytokinesis. The end result of mitosis is the formation of two identical daughter cells that are diploid (have a full set of chromosomes [2 n]). Mitotic cell division: The parent cell divides to form 2 daughter cells with the same number of chromosomes 2 n=46. – For example: A human cell has 46 chromosomes. How many chromosomes will it have after mitotic cell division? __46_______

State Test Question A frog cell has 26 chromosomes. After the first mitotic division, the cells produced by the zygote will have— a) 52 chromosomes. b) 39 chromosomes. c) 26 chromosomes. d) 13 chromosomes

Here are the four stages of Mitosis: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Prophase (P) a. Stringy chromatin coils up into chromosomes. b. Chromosomes are most easily seen during this phase because the chromatin shortens and thickens. c. Each duplicated chromosome is made of the two halves called sister chromatids. d. Nuclear membrane disintegrates (disappears) e. Spindle forms between the pair of centrioles which begin to move to the opposite end (poles). Spindle fibers are cell structures made up of both centrioles and individual microtubule fibers that are involved in moving chromosomes during cell division. Centrioles help anchor spindles for movement of chromosomes. The spindles pull the chromosomes to opposite sides of the cell.

iv. As each pair of centrioles migrate to their respective poles, they pull one set of microtubule ends after them. v. The other set of ends are connected to the opposing halves of each sister chromatid. The spot of attachment on each centromere half is termed the kinetochore. vi. Microscopically, the centrioles and their associated microtubules somewhat resemble vii. The appearance of the 2 asters, with their microtubules radiating to the cell's equator, is known as the Mitotic spindle (metaphase plate). viii. The chromosomes are very distinct and are used for genetic studies at this stage.

State Test Question Chromosomes are most easily seen during cell division because the chromosomes-a) double in number. b) shorten and thicken. c) move and expand. d) match up with other chromosomes

State Test Question Which of the following does NOT occur during interphase? a) Chromosomes become visible b) Proteins synthesize c) Chromosomes duplicate d) Proteins translocate

The Cell Cycle Metaphase (M) • Chromosomes line up along the equator. (Centromeres are attached to the spindle fibers. )

State Test Question Which phase of mitosis is represented by the diagram shown above? a) Metaphase b) Prophase c) Telophase d) Interphase

The Cell Cycle Anaphase (A) a. Centromeres split separating chromatids. Chromosomes are now called chromatids. b. Chromatids move toward opposite poles.

The Cell Cycle Telephase (T) a) The identical chromatids, now chromosomes, reach opposite poles. b) Nuclear membrane reappears c) Spindles disappear d) Chromosomes uncoil into threadlike pieces e) DNA is now called chromatin

As mitosis ends, cytokinesis begins. Cytokinesis: Divides the cytoplasm and organelles between the two new cells. **New daughter cells will enter into Interphase to begin the cycle over again.

State Test Question • a) b) c) d) Which phase of the cell cycle involves replication of chromosomes? G 1 of interphase The synthesis phase of interphase Prophase Cytokinesis

State Test Question • a) b) c) d) Following telophase, two daughter cells are created when new membranes are formed in the process called— interkinesis. cytokinesis. chromosome replication. crossing over.

State Test Question Lab Notes▪ Chromatids have been separated ▪ The cytoplasm is separating▪ A visible line is forming between sets of chromatids Which phase of mitosis is being described in the lab notes shown above? a) Telophase b) Anaphase c) Metaphase d) Prophase

State Test Question The stages of cell division called prophase, metaphase, and telophase occur during which stage of the cell cycle shown in the diagram below? a) G 1 b) S c) M d) C

State Test Question Which event in mitosis has NOT yet occurred? a) Chromosomes lining up b) Spindle fibers shortening c) Chromosomes duplicating d) Cytoplasm dividing

What are the differences in animal cells and in plant cells undergoing mitosis? 1. Plant cells do NOT have centrioles 2. Plant cells divide their cytoplasm with a cell plate. 3. In animal cells, cytokinesis begins with a cleavage furrow, which pinches the cell into 2 cells. 4. A cleavage furrow forms--the precursor of the cell membrane. 5. This furrow deepens forming a contractile ring until two new cells develop, each with a complete nucleus. Centrioles

The Cell Cycle Factors that control the cell cycle: • The cell cycle is carefully controlled. Failure of cellular control can result in cancer. • Cancer is the uncontrolled growth of cells. Cancer is a disorder of cell division. • Cancer is a mistake in the cell cycle. • Cancer is one result of uncontrolled cell division. • The loss of control may be caused by environmental factors or by changes in enzyme production. • Cancerous cells affect normal cells, forming masses of tissue called tumors that deprive normal cells of nutrients. In the final stages, cancer cells enter the circulatory system and spread throughout the body forming new tumors that disrupt the functioning of organs. Lung Cancer Cells

State Test Question Which of the following BEST describes the purpose of mitosis? a) The production of a complete copy of the nucleus before cell division b) The division of the cell after the nucleus has been copied c) The production of gametes with half the number of chromosomes of a normal cell d) The replication of DNA within the nucleus

State Test Question Which of the following process is MOST responsible for getting genetic information to each cell in the body of an organism? a) Protein synthesis b) Mitosis c) Diffusion d) Respiration