BIO.B.1.2 – Explain how genetic information is inherited. DNA and Cell Division BIO.B.1.2 – Explain how genetic information is inherited.

DNA facts There’s an estimated 3 billion DNA bases in our genome. One million bases (called a megabase and abbreviated Mb) of DNA sequence data is roughly equivalent to 1 megabyte of computer data storage space. Our entire DNA sequence would fill 200 1,000-page New York City telephone directories. A complete 3 billion base genome would take 3 gigabytes of storage space. If unwound and tied together, the strands of DNA in one cell would stretch almost six feet but would be only 50 trillionths of an inch wide. In humans, the DNA molecule in a non-sex cell would have a total length of 1.7 meters If you unwrap all the DNA you have in all your cells, you could reach the moon 6000 times! If all the DNA in your body was put end to end, it would reach to the sun and back over 600 times (100 trillion times six feet divided by 92 million miles). Over 99% of our DNA sequence is the same as other humans’. The average gene is 10,000 to 15,000 bases long.

How is genetic information inherited?....DNA Genetic information is passed from one cell to the next by a molecule called DNA. DNA is located inside chromosomes within the nucleus of a cell. What does DNA stand for? Deoxyribonucleic Acid. DNA is a nucleic acid made of two strands of nucleotides wound together in a spiral called a double helix. Each nucleotide is composed of the following: 1.) a sugar molecule known as deoxyribose 2.) a phosphate group 3.) one of four different nitrogenous bases: adenine (A) thymine (T) guanine (G) cytosine (C)

DNA Structure The nitrogen containing bases are the only difference in the four nucleotides. DNA structure is the same in all organisms. The DNA of different organisms differs ONLY in the sequence of nucleotides. The differences in nucleotide sequence are responsible for the genetic differences between organisms. These nucleotide sequences hold the code used to make proteins.

DNA Structure Watson and Crick determined the three-dimensional structure of DNA by building models. They realized that DNA is a double helix that is made up of an alternating sugar-phosphate backbone on the outside with nitrogen bases on the inside.

DNA Structure Nucleotides always pair in the same way. They follow Chargaff’s rule, also known as the base pair rule, which states…. A binds with T C binds with G Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. The backbone (sugars and phosphates) is connected by covalent bonds. The bases are connected by hydrogen bonds. hydrogen bond covalent bond View this video on DNA Basics!

DNA Replication DNA Replication is the process in which DNA makes an exact copy of itself. A single strand of DNA serves as a template (pattern) for a new strand. Replication occurs following the base-pair rules (A = T and C = G). DNA is replicated during Interphase (S – Synthesis) of the cell cycle. Each somatic cell (body cell) gets a complete set of identical DNA.

DNA Replication DNA Replication is semi-conservative which means that the DNA molecule uncoils and separates into two strands. Each original strand becomes a template on which a new strand is constructed, resulting in two DNA molecules identical to the original DNA molecule. One strand is part of the original parent strand and one strand is a newly formed strand…hence the name semi-conservative (one strand was conserved).

The DNA molecule unzips in both directions. Step 1: The enzyme helicase unzips DNA in multiple locations within the DNA double helix. nucleotide The DNA molecule unzips in both directions. There are many origins of replication in eukaryotic chromosomes.

Step 2: Nucleotides floating within the nucleus of the cell attach to complementary nucleotides from the original unzipped strands. The enzyme DNA polymerase bonds new and original nucleotides together. DNA polymerase new strand nucleotide

Step 3:Two new molecules of DNA are formed, each with an original strand and a newly formed strand. Once again, this is why we say replication is “semi-conservative.” original strand new strand Two molecules of DNA The enzyme DNA polymerases can also find and correct errors to prevent mutations from occurring.

Cell Division Mitosis vs. Meiosis BIO.B.1.1.1 – Describe the events that occur during the cell cycle interphase, nuclear division (mitosis and meiosis) and cytokinesis.

Chromosome Structure Chromosomes – a single piece of coiled DNA and proteins found in eukaryotic cells and prokaryotic cells. Each organism has a specific number of chromosomes. How many chromosomes are in human somatic (body) cells? ______ How many chromosomes are in a prokaryotic cell? ______________

Chromosome Structure Continued… Chromosomes contain genes that code for specific traits (eye color, hair color, etc…). View this video entitled “What are genes?”

Chromosome Structure Continued… Uncondensed (uncoiled) DNA plus proteins is called chromatin. One half of a duplicated chromosome is a chromatid. Sister chromatids are held together at the centromere. chromatid Condensed, duplicated chromosome centromere Check out this link on “Chromosome Basics.”

The Cell Cycle The cell cycle is a series of events that take place in EUKARYOTIC cells. There are three main events that occur during the cell cycle. These events include: 1. Interphase – preparation for cell division 2. Nuclear Division – division of the nucleus 3. Cytokinesis – division of the cytoplasm

The Cell Cycle Interphase consists of 3 phases: What happens during the cell cycle? Interphase – the longest part of the cell cycle in which a cell performs the majority of its functions, such as preparing for nuclear division and cytokinesis. Interphase consists of 3 phases: Gap 1 (G1) - Cell growth, normal functions, organelles duplicate Synthesis (S) - DNA replication (Synthesis of DNA) Gap 2 (G2) - Additional growth 2. Nuclear division – division of the nucleus There are two types of nuclear division: Mitosis – a nuclear division that results in 2 somatic (body) cells with identical DNA. Meiosis – a two-phase nuclear division that results in the production of 4 gametes (sex cells) that are genetically different. 3. Cytokinesis - division of the cytoplasm

Nuclear Division: Mitosis vs. Meiosis

The Cell Cycle Checkpoints in the cell cycle will only allow the cell to divide if the cell is large enough and the DNA is undamaged! The surface area of a cell must be large enough for the transport of materials into and out of the cell. Cells that are large tend to have different shapes to help them function properly. The rate of cell division varies depending upon the location and function/type of the cell. Some cells are unlikely to divide, such as neurons (nerve cells). These cells stay in a phase known as (G0).

How do cells know when to divide? 1.)Injury…Cells know when repair is necessary because they rely on cell to cell contact. If a cell is missing they will start to divide until they come into contact with other cells. 2.)Growth factors…Growth factors are types of proteins present in organisms that stimulate a cell to divide. 3.) Cyclins…Cyclins are proteins found within cells that help to control the cell cycle.

Uncontrolled Cell Division Uncontrolled cell division results in tumors. Tumors can be malignant OR benign. Malignant tumors are cancerous and can metastasize within an organism. Cancer cells do NOT carry out necessary functions. Cancer cells come from normal cells with damage to the genes that are involved in cell cycle regulation. Carcinogens are substances that cause these gene mutations.

Mitosis Mitosis = Division of nucleus  Forms 2 somatic cells Somatic cells = all body cells except sex cells/gametes What are some examples of somatic cells that undergo mitosis? Are somatic cells genetically identical? Do they have the same DNA?

Interphase -Preparing a cell for division Parent cell centrioles spindle fibers centrosome nucleus with chromatin (contains DNA) Interphase prepares the cell to divide by growing and duplicating the DNA. Chromatin and a nuclear membrane are both visible.

Prophase – 1st stage of mitosis During prophase, chromatin condenses to form chromosomes and spindle fibers form. The nuclear membrane begins to dissolve.

Metaphase – 2nd stage of mitosis During metaphase, chromosomes line up in the middle of the cell attached to spindle fibers.

Anaphase – 3rd phase of mitosis During anaphase, sister chromatids separate and travel to opposite sides of the cell.

Telophase – 4th & final stage of mitosis During telophase, two new nuclei form and chromosomes begin to uncoil.

Cytokinesis – division of the cytoplasm Cytokinesis differs in plant and animal cells. In animal cells, the plasma membrane pinches closed. In plant cells, a cell plate forms.

Cell Differentiation Although all somatic cells contain the same DNA they may perform different functions in an organism. This is due to a process called cell differentiation, in which a cell will develop into its mature form based on the DNA (genes) that is expressed (read). Cells that perform similar functions are called tissues. Tissues that work together to perform specific functions are called organs. Organs that work together to perform specific functions form an organ system.

Stem Cells Stem cells are special cells that have the ability to: divide and renew themselves remain undifferentiated in form develop into a variety of specialized cell types Stem cell research has the potential to change medicine. Why?

Asexual Reproduction Asexual reproduction is the creation of offspring from a single parent. It forms offspring identical to the parent. Environment determines what form of reproduction is most advantageous. For example: Asexual reproduction is an advantage because organisms d0 not need to waste time and energy looking for a mate. Asexual reproduction occurs more quickly than sexual reproduction. A disadvantage to asexual reproduction is that genetically identical organisms are produced; therefore during unfavorable conditions an entire population can be harmed.

Asexual Reproduction in Prokaryotes All prokaryotes reproduce asexually by a process known as binary fission. Binary fission is the splitting of a parent cell into two genetically identical daughter cells. How is it similar to mitosis? How is it different? (Look at the diagram.)

Asexual Reproduction in Eukaryotes Some eukaryotes can reproduce asexually by mitosis. There are different types of mitotic reproduction which include: Budding (Yeast – diagram 1) Fragmentation/Regeneration (Planaria – diagram 2) Vegetative Propagation (Strawberries – diagram 3)

Budding Budding - forms a new organism from a small projection growing on the surface of the parent. bud Hydra Yeast

Fragmentation OR Regeneration Fragmentation or (regeneration) is the splitting of the parent into pieces that each grow into a new organism. Can you think of any organisms that regenerate?

Vegetative Propagation Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant. Do you know of any plants that use vegetative propagation to reproduce?

Sexual Reproduction During sexual reproduction offspring are formed from two parents. Both parents produce sex cells called gametes. Male Gamete vs. Female Gamete SPERM EGG Fertilization must occur for sexual reproduction to be successful. Fertilization is the joining of a sperm and an egg.

Types of Cells Body cells are also called somatic cells. They are formed by MITOSIS. Somatic cells are located throughout the body (heart, brain, stomach, lung, skin, etc…) DNA in your somatic cells is NOT passed on to your children. Germ cells develop into gametes. They are formed by MEIOSIS. Germ cells are located in the ovaries and testes. DNA in your gametes IS passed on to your children.

Haploid vs. Diploid Cells Somatic cells (body cells) are diploid cells. Diploid cells (2n) have two copies of every chromosome. One copy comes from your mother and one copy comes from your father. Gametes (sperm and eggs) are haploid cells. Haploid cells (n) have one copy of each chromosome. What is the human haploid number? (n = 23) Diploid number? (2n = 46) Mitosis makes diploid cells. Meiosis makes haploid cells.

Types of Chromosomes All cells contain DNA located in chromosomes. Cells have two types of chromosomes: Autosomes: Non-sex chromosomes (Pairs 1-22) Sex Chromosomes: Chromosomes that contain genes related to your sex. (Pair 23) XX = female XY = male Karotype – picture of all the chromosomes in a diploid cell.

Homologous Chromosomes Homologous chromosomes: Chromosomes that have the same structure and contain the same genes in the same locations. In a homologous pair of chromosomes, one chromosome is inherited from mom and one chromosome is inherited from dad. View this video entitled “Where do your genes come from?”

Meiosis Meiosis = A type of nuclear division that divides a diploid cell into four haploid cells. Meiosis is the process that forms gametes (sperm and eggs); therefore it is necessary for sexual reproduction to occur.

Meiosis Germ cells (46 chromosomes) undergo two rounds of cell division, which results in cells with a reduced number of chromosomes (23 chromosomes). Interphase occurs before Meiosis I (the first division) but DOES NOT occur before Meiosis II (the second division). Meiosis increases genetic variation and diversity.

Stages of Meiosis I What is a tetrad? Homologous chromosomes line up together to form tetrads in a process called synapsis.

Check out these meiosis videos: Stages of Meiosis II Check out these meiosis videos: Video #1 Video #2

Name That Phase!

Crossing Over Crossing over: An exchange of genetic material between homologous chromosomes during prophase I of meiosis. Crossing over increases genetic variability (differences) in gametes.

Quiz yourself at neok12.com/Cell-Division.htm Mitosis Vs. Meiosis Mitosis has one cell division. Meiosis has two cell divisions. During meiosis homologous chromosomes pair up. During mitosis homologous chromosomes never pair up. Quiz yourself at neok12.com/Cell-Division.htm

Gametogenesis Where does MEIOSIS occur???? Meiosis occurs in organs called gonads. Female gonads are ovaries. Male gonads are testes. Inside the gonads are germ cells. Germ cells produce gametes by the process of meiosis. Female germ cells = oocytes Male germ cells = spermatocytes Oocytes are formed by a type of meiosis called oogenesis. Spermatocytes are formed by a type of meiosis called spermatogenesis.

Oogenesis Vs. Spermatogenesis

Reproductive Organs MALE FEMALE

Fertilization and Beyond….. 1st: Fertilization – joining of sperm and egg 2nd: Growth and Development – occurs by the process of MITOSIS Zygote Embryo  Fetus  Infant

Embryo  Fetus  Infant

Pregnancy & Birth

Advantages to Sexual Reproduction Greater variety/diversity in organisms. Greater ability to adapt and evolve. Disadvantages: Requires more energy than asexual reproduction. Requires more time (finding a mate) than asexual reproduction.