Chapter 4 Notes Genes and DNA 4.1 What does DNA Look Like? Genes are part of the chromosome. Chromosomes are made of protein and DNA. DNA is the genetic material that determines inherited characteristics. DNA is made of smaller components known as nucleotides. Each nucleotide is made of sugar, phosphate and a base.
Each nucleotide is the same except for the base. The four bases are: adenine (A), Thymine (T), Guanine (G) and Cytosine ( C ). Chargaffs Rule states that the amount of adenine is always based with and equal to thymine. The amount of cytosine is always based with and equal guanine. Rosalind Franklin used x-ray diffraction to make images that helped lead to the discovery of the shape of DNA.
Watson and Crick used Franklins work to discover that DNA has a twisted ladder shape (double helix). This also helped explain how DNA is copied and how it functions in the cell. When DNA replicates (is copied) the base pairs will only pair up with the complementary base (A to T, C to G). When DNA is being copied it is similar to the DNA being unzipped and rezipped up with a new set of bases. Again the bases matching with the correct complementary base.
4.2 How DNA Works Refer to Figure one on page 90 in your text as to how DNA is unwound and gets ready for cell division. The DNA code is read like a book. Different groups of three bases equate to different codes for amino acids. For example different letters of the Latin alphabet put together make up different Roman numerals. VII= 7, XXX=30, III=3. A long string of amino acids form a protein. Such as multiple letters
equal a larger number. Proteins are the messengers for many processes in the cell. RNA also helps make proteins . See figure 2 on page 92-93. RNA Simplified: Look at steps and relate to the example Step 1- copy of DNA of a gene is transferred to RNA, just like going to McDonalds and verbally ordering a meal and the worker typing it into the register.
Step 2 and 3- The mirror RNA is called mRNA (messenger RNA) and each group of three bases form code for an amino acid, just like ordering a #1 and it includes a hamburger, fries and a drink. Step 4- the mRNA is fed through the ribosome, the cooks at McDonalds receive your order in the kitchen from a computer. Step 5: Molecules transfer RNA (tRNA). Your food items are all made and put on a tray. Step 6: Amino acids are dropped off at the ribosome. Your food is
dropped off item by item at your table. Step 7: Amino acids join together to make a protein. All items together (hamburger, fries and drink) make your complete meal. Mutations occur when the DNA does not copy correctly. Three types of mutations. Deletion- a base is missing in a pair. Insertion-an additional base is added. Substitution- the wrong base is used.
Genetic Engineering is when scientists manipulate the gene to create; better, new or altered organisms. Each organisms DNA is unique to them. A personal blueprint/identification. The exception to this would be identical twins. One egg and sperm split during mitosis to create two identical embryos rather than one. Meaning that identical twins are clones of one another. Clones have also been recreated by scientists in a lab. Dolly, the sheep, one of the most famous clone created. Since then, scientists have been
perfecting and cloning more organisms, including peoples pets.
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