DNA - Structure and Function ~ Deoxyribonucleic Acid ~

Recap – Nucleic Acids Nucleic Acid is a category of biomolecules that includes DNA, RNA, and ATP DNA – Deoxyribonucleic Acid RNA – Ribonucleic Acid ATP – Adenosine Triphosphate The building block of a nucleic acid is a nucleotide: Sugar Phosphate Nitrogenous base

Dna – Genetic Instructions DNA is a double helix – “spiral staircase” The sugar and phosphate molecules make up the backbone, or hand railing of the DNA “spiral staircase”. The sugar and phosphate molecules of the DNA double helix are held together by strong phosphodiester bonds, more commonly known as covalent bonds. These bonds have to be STRONG COVALENT BONDS because the sugar and phosphate backbone (hand railing) has to help protect the sequence of bases in the center of the double helix, and help the DNA double helix maintain its structure.

Dna – Genetic Instructions DNA is a double helix – “spiral staircase” continued… The nitrogenous bases make up the stair steps of the DNA double helix. The sequence of nitrogenous bases ARE an organism’s genetic code. The nitrogenous bases are protected inside the sugar and phosphate backbone and the double helix structure. The nitrogenous bases of DNA are: Adenine Guanine Cytosine & Thymine DNA bases always bond in a specific way: Adenine bonds to Thymine Guanine bonds to Cytosine

Dna – Genetic Instructions DNA is a double helix – “spiral staircase” continued… The nitrogenous bases of the DNA double helix are held together by weak hydrogen bonds. These bonds have to be WEAK HYDROGEN BONDS because the nitrogenous bases have to be easily “unzipped” for DNA replication and protein synthesis (we will learn about both of these later). DNA is double stranded (double helix), and the two strands of DNA are antiparallel to each other…parallel but moving in different directions.

DNA…a Reminder and For future reference All living organisms have DNA made up of the same four nitrogenous bases…Adenine, Guanine, Cytosine, and Thymine…the sequence is just different. Nitrogenous bases are responsible for all organisms’ genetic code. The central dogma of biology… DNA → RNA → Proteins What should this mean to you?? DNA does not only hold an organism’s genetic code, it is the instructions for the construction of all proteins in an organism… (we will learn about this very soon)     

Cell Cycle & Mitosis What is the cell cycle? Cell cycle is the life cycle of a cell… The cell cycle is a process in which a cell grows and divides to create a copy of itself. Some organisms reproduce exclusively through this process, while in complex multicellular life, it allows an organism to grow, and to replace cells as they become worn out.

Interphase is made up of G1, S, & G2 phases…

You need to memorize the Cell Cycle and what is going on in each step. You also should recognize the amount of time spent in each step of the Cell Cycle. Interphase is the longest phase of the cell cycle (G1, S, G2). Cells spend a relatively short amount of time in mitosis.

What is Mitosis? Mitosis is nuclear division (division of the nucleus) It can be broken down into Prophase, Metaphase, Anaphase, and Telophase. Mitosis is followed by Cytokinesis, or division of the cytoplasm. You should be able to recognize and label the phases of mitosis, and recognize what is happening to the DNA in each phase (what it looks like).

Remember!!! Mitosis produces two identical cells from a single parent cell. Two cells produced are called daughter cells. Daughter cells are genetically identical to the single parent cell. Occurs in somatic cells in humans (regular body cells)