DNA, Mitosis, and Meiosis Learning Target Objectives: I can…  Describe the structure of, base pairing, and roles (importance) of both DNA and RNA.  Explain the processes and locations of replication, transcription, and translation.  Compare and contrast mitosis and meiosis, describing in detail each phase of the cell cycle for each.  Differentiate between chromatin, chromatids, and chromosomes and between homologous chromosomes and sister chromatids. Vocabulary: DNA * deoxyribose * nucleotide * base * purine * adenine * guanine * pyrimidine * thymine * cytosine * Rosalind Franklin * Watson & Crick * hydrogen bonding * complimentary base * replication * transcription * uracil * gene * chromatin * histone * chromosome * chromatid * centromere * homologous chromosomes * diploid * 2N * haploid * 1N * mitosis * cell cycle * interphase * prophase * metaphase * anaphase * telophase * cytokinesis * synapsis * tetrad * crossing over * meiosis

DNA – deoxyribonucleic acid - stores & uses information needed to direct cell activities - makes exact copies of itself for new cells - composed of nucleotides in 2 long strands wrapped in a double helix (like a twisted ladder) Nucleotides – each has 3 parts: 1) a 5-carbon sugar called deoxyribose 2) a phosphate group (PO 4 ) 3) A nitrogenous base (1 of 4 available)

Types of Bases: 1) Purines – have 2 Carbon with Nitrogen rings. Purines: 1) adenine 2) guanine 2) Pyrimidines – have 1 Carbon/Nitrogen ringPyrimidines: 1) thymine 2) cytosine

Three scientists important to the discovery of DNA structure: 1) Rosalind Franklin 2) James Watson 3) Francis Crick The Double Helix The sides of the “ladder” are made of alternating molecules of deoxyribose (a 5 carbon sugar) and phosphate (PO 4 ). The “rungs” of the ladder are formed by 1 purine joining 1 pyrimidine base by hydrogen bonding (requires N, O, or F) The base always forms pairs of: A to T or C to G with 2 hydrogen bonds between A and T but 3 hydrogen bonds between C and G. These are considered complimentary bases. A = T C = G

There are ten base pairs in every twist of the DNA. This makes it very uniform. The bases always bond to the sugar along the sides of the DNA and the phosphate binds between sugar molecules toward the outside of the DNA. DNA Replication Exact copies of the DNA are made by “unzipping” the ladder part way at many locations at once. Then the compliment to the existing base floats into place. This creates two DNA molecules. Each has one newly formed DNA strand and one old strand. Enzymes unzip DNA, glue the separate copied pieces together to form 1 strand, and repair damage in existing DNA.

All genetic information is held in the sequence of DNA bases! Our traits (Ex: hair color, eye color, etc.) are determined by proteins. Proteins are made by RNA (ribonucleic acid) RNA is made from DNA. RNA is: A single strand Has ribose as its 5-carbon sugar Substitutes uracil for thymine when copying DNA codes Production of RNA from DNA is called transcription. Each set of three bases (called a codon) on 1 mRNA codes for 1 amino acid. The order in which the amino acids are coded will determine which protein forms. Remember, proteins are made at the ribosomes! DNA to DNA = replication DNA to RNA = transcription

Gene – region of DNA that codes for a certain protein polypeptide. Since proteins are made of many polypeptides, many genes may be needed to make 1 protein All life comes from a single cell or a single fused cell (sperm & egg) by cell division. This requires DNA replication. DNA is found on chromatin within the nucleus of the cell. When cell division occurs, replicated strands of DNA (on chromatin) begin condensing and coiling around special proteins known as histones. Once this is done, the chromatin/histone complex is called a chromosome.

Chromosomes are made of 2 dense strands called chromatids. Since they are identical, they are called “sister chromatids.” They join each other at an area called the centromere. Review Chromatin – thin, uncoiled, loose strands of DNA Chromosome – dense replicated strands of DNA coiled around histone as cell division begins Chromatid – “sister” strands joined at a centromere to form a chromosome (contain DNA)

Homologous chromosomes – each chromosome has a partner chromosome (from the opposite parent) of the same size and shape (the homologue). All species have a set number of chromosomes for that species. This number is different for different species. Humans have 46 chromosomes (23 pairs) in each cell except egg and sperm cells. Diploid cells – contain both partners of a homologous pair (2N) Haploid cells – have only 1 chromosome from each pair (1N) Ex: eggs and sperm

Mitosis – division of cell nucleus. The parent cell’s chromosomes divide into 2 identical sets. In asexual reproduction, this is how a new organism forms. The Cell Cycle 1) Interphase – the cell increases in size, doubles the number of organelles present, the DNA (on chromatin) replicates. Cells spend most of their “lifetime” in interphase. 2) Mitosis: a) Prophase – - chromatin coils to form chromosomes - nuclear membrane disappears - spindle fibers extend from centrioles b) Metaphase – - chromosomes line up in the middle of the cell c) Anaphase – - sister chromatids separate at centromere & move to opposite sides of the cell d) Telophase – chromatids at opposite poles of the cell unwind into chromatin - nuclear membrane forms around chromatin

3) Cytokinesis – the cytoplasm splits, separating the 2 nuclei and the replicated organelles into 2 new cells of about equal size. Mitosis produces 2 daughter cells with 2N (asexual reproduction including that of ALL of our cells except egg & sperm). Cells are virtually identical. Meiosis – produces 4 (non-identical) daughter cells with 1N. This is necessary for egg & sperm in sexual reproduction or the offspring would end up with too many chromosomes. This is the result of 2 nuclear divisions instead of one. Meiosis I – homologous chromosomes separate into 2 new cells Meiosis II – sister chromatids separate into 2 new cells.

During Meiosis I – Prophase I differs from mitosis prophase because homologous pairs of chromosomes pair up (synapsis) forming a tetrad. (group of 2 chromosomes which means 4 sister chromatids are present) This allows for crossing-over of chromatids with genes (pieces of chromosomes) being exchanged. (more genetic variability). Sexual reproduction produces offspring unlike either parent due to new combinations of genes.

Replication, Transcription, and Translation During interphase, the cell is NOT resting as once thought. It is either: 1) duplicating DNA (replication) in preparation for cell division (mitosis or meiosis) or, 2) it is actively preparing to make proteins for growth and repair In order to make proteins, the DNA must unzip in the region coding for the desired protein, then an RNA compliment to the DNA must be made. (This is called transcription.) Here a single strand of messenger RNA, also known as mRNA is created by binding an adenine to an existing thymine, a cytosine to a guanine, guanine to cytosine, and uracil to adenine (instead of the thymine used when making DNA). mRNA leaves the nucleus and once the it reaches a ribosome, it is “translated.” Translation is when the ribosome reads mRNA and begins linking amino acids together to form a polypeptide, and then a protein. Every 3 letters (A, C, G, and/or U) forms a codon on the mRNA this has a complimentary anti-codon on the transfer RNA that carries the amino acid to be added to the protein