The Structure of DNA

What is DNA? DNA - deoxyribonucleic acid Holds all our cell’s information Code for proteins that are essential for life

Where is it located? DNA is found in the nucleus DNA is packaged into units known as chromosomes Short sections of DNA are referred to as genes Genes carry the instructions to make specific proteins Proteins are what make up the characteristics of an organism.

Human Genome All of an organisms DNA is referred to as its genome The human genome contains 23 pairs of chromosomes in almost every cell of the body One pair of chromosomes determines the sex of an individual. In males, the 23rd chromosome is the XY pair and in females, it is the XX pair.

Structure of DNA DNA has double strands and consists of smaller molecules called nucleotides. DNA looks like a spiral shape that scientists refer to as a double helix (looks like a twisted ladder). A nucleotide is composed of three parts: Deoxyribose Sugar Molecule Phosphate Molecule Nitrogenous Base

Nitrogenous Bases 1. Adenine 2. Guanine 3. Cytosine 4. Thymine Each Nucleotide has one of the four different nitrogenous bases: 1. Adenine 2. Guanine 3. Cytosine 4. Thymine Pairs of bases form a rung of the DNA ladder

Base Pairing Rule Adenine always pairs with Thymine (A-T) Cytosine always pairs with Guanine (C-G) Between each pair is a hydrogen bond that holds the pairs together.

DNA replication One thing that makes DNA so amazing, is its ability to copy itself. Before a cell divides, each DNA molecule makes a copy of itself. DNA splits down the middle like a zipper and new bases join up with bases on each of the open ends. The result is two new identical DNA strands. Each new DNA molecule has one new strand and one old strand.

DNA unzipping Nucleotides pair up according to the base pairing rules Example: The “Thymine” will pair up with a new “Adenine” molecule The two new DNA molecules are identical and each has an old and a new strand.

Two new identical DNA strands

Genetic Code The bases in DNA molecules are like the numbers and letter in a Code. DNA has a four character code. The four characters are the Nitrogenous bases: A, T, G, C The bases combine to form a three letter word called a ”CODON”, example ATG, CTA, TGA, etc… Thus, when a DNA is replicated it has to follow the same three combinations throughout the DNA strand.

Genetic Code Each 3 letter word (CODON) codes for the production of one of the 20 amino acids Amino Acids are the Building Blocks of Protein. Different combinations of amino acids results in the formation of different proteins. The proteins determine the characteristics of an organism.

Protein synthesis There are several steps involved in making a protein from DNA Transcription is when RNA is made from DNA. The information is copied from one molecule to the other.  Translation converts a mRNA (messenger rna) sequence into a string of amino acids that form a protein. 

Different Types of Proteins Function Hemoglobin Carries oxygen in red blood cells Insulin Controls the level of sugar in the blood Keratin Makes up hair and nails Enzymes Controls chemical reactions in the body Antibodies Bind to foreign substances to protect the body against the foreign substance Growth Hormone Stimulates growth (cell division)

Transcription 1) DNA Unzips. 2) One strand of DNA is used to make another molecule called messenger ribonucleic acid (mRNA). The mRNA copies info from DNA using base pairings. 3) mRNA carries the genetic code from the nucleus to the ribosome in the cytoplasm

How is RNA different from DNA? Single stranded, not double stranded Sugar - Instead of deoxyribose, it has ribose Base Pair - Instead of Thymine, it uses Uracil (Now A pairs with U)

Translation 1)  rRNA (ribosomal RNA) attaches to mRNA and starts reading the codons (3 nucleotides at a time) to produce one amino acid. 2) tRNA (transfer RNA) carries the produced amino acids and attaches them to the correct part of the growing amino acid chain. The chain is also known as a polypeptide. 3) When protein production is complete (the string of amino acids), the ribosome releases the protein chain (polypetide).

Protein Synthesis Review

Video Video on DNA Replication Video on Transcription and Translation. https://www.youtube.com/watch?v=9kp9wiYMQUU&list=PLybg94GvOJ9Fazvaf8unWl9J2soXCAvy4&index=12 Video on Transcription and Translation. https://www.youtube.com/watch?v=bKIpDtJdK8Q&list=PLybg94GvOJ9Fazvaf8unWl9J2soXCAvy4&index=13

Assignment Science Probe 9 – Page 47, Questions 1 – 16 exclude #9, #10, and #11.