UNIT A IN YOUR GRADE 9 SCIENCE 9 PROBE TEXTBOOK UNIT 1: REPRODUCTION UNIT A IN YOUR GRADE 9 SCIENCE 9 PROBE TEXTBOOK
2.3 From DNA to Proteins (pg. 42) The nucleus contains the chromosomes which are made of DNA. DNA contains the instructions for the body. How does the body read the instructions and build the body?
Lets understand DNA Shape – DNA is made up of nucleotides (Fig 1 pg 42). The nucleotides pair up to form ladder rungs. There are four types: Adenine (A) goes with Thymine (T), Cytosine (C) goes with Guanine (G). The ladder shape then twists to form a helix. Copying – DNA can unzip and then new nucleotides attach to each side of the original. In the end you end up with two new DNA each with half of the original in them. (see page 43)
Lets understand DNA https://www.youtube.com/watch?v=8kK2zwjRV0M Genetic Code – So how do the base pairs (A, T, C, G) contain information? In three letter “words” called codons. Each codon codes for the production of 1 of 20 amino acids. A chain of amino acids is a protein. Genes – All of your DNA is organized into 23 chromosomal pairs. These are like encyclopedias that contain instructions on how to make all the proteins in a body part. A single gene is the instructions for how to make a single protein. https://www.youtube.com/watch?v=8kK2zwjRV0M
How does the Genetic code become a body part? Finding the right gene – First the DNA unwinds the chromosome so that a copy of the needed gene can be made. This is copy is called RNA (ribonucleic acid). RNA is similar to DNA except it is only one strand. RNA to Ribosome – The RNA then leaves the nucleus and attaches to a ribosome which “reads” the code on the RNA. Ribosome builds the Protein – As the RNA reads the code it attaches the amino acids in the order listed. This builds the protein.
Gene Variation Not everyone looks the same. This is because the instructions in the genes can vary slightly from person to person. You have two copies of each gene, one from your Mom and one from your Dad. One of these will show up and the other will be hidden (recessive).