Chapter 11: DNA- The Molecule of Heredity

Do now : Living things contain proteins. Your skin, muscles, and bones contain protein. All the actions you perform such as eating, running, and thinking depend on proteins called enzymes. How is this related to DNA?

DNA determines the structure of proteins Provide complete instructions for making proteins Made up repeating units called nucleotides

DNA in Cells Located in the nucleus of cells as chromosomes Packed tightly Consists of more than 30 million base pairs Complimentary DNA strands Can use 1 strand to make a copy of the other strand using base pairing

Nucleotides Make up DNA 3 parts to a nucleotide: A simple sugar A phosphate group A nitrogen base

Nitrogen Bases A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen 4 possible nitrogen bases: Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

Adenine (A) and Guanine (G) Double-ringed nitrogen bases Called purines

Thymine (T) and Cytosine (C) Single-ringed nitrogen bases Called pyrimidines

Structure of DNA long zipper that is twisted into a coil like a spring. Something twisted into a coil is called a helix. DNA is made of two strands that are twisted into a coil, so it is called a double helix.

How can DNA do so much with so little? The key to variety in organisms is the sequence, or order, of the four nucleotides. Ex: A-T-T-G-A-C carries different information than the sequence T-C-C-A-A-A. EAT ATE TEA

DNA Replication Making a copy of DNA DNA is copied before cell division During the S phase of interphase DNA will separate into 2 strands Unzips DNA by breaking hydrogen bonds to unwind the double helix Makes new complimentary strands through base-pairing

After DNA is replicated, DNA will have 1 old strand and 1 new strand

What is the role of RNA in a cell? Think of a car factory and an assembly line. A car is a complicated piece of machinery. But cars are built by following simple steps. Engineers tell workers how to make the cars, and workers follow the directions to build the cars on the assembly line. Suppliers bring parts to the assembly line so they can be used to build the cars. This is similar to the role of DNA and RNA in a cell. DNA gives the instructions to make proteins. Workers build proteins. Other workers bring the parts, in this case, amino acids, to the assembly line. In our example the workers are the RNA. Just as in a typical factory, workers have specific tasks. So does RNA

What does RNA look like? nucleic acid. RNA is a single strand. instead of thymine, RNA has uracil. In RNA uracil (U) binds with adenine.

Example: DNA mRNA A G C T

Example: DNA mRNA A G C T U C G A

Transcription First, a portion of the DNA molecule unzips. Free RNA nucleotides pair with the nucleotides on the DNA strand. The mRNA strand is complete when the RNA nucleotides form a strand by bonding together. The mRNA strand breaks away and the DNA strands rejoin. The mRNA strand leaves the nucleus and enters the cytoplasm.

Messenger RNA (mRNA) Brings instructions from DNA out of the nucleus and into the cytoplasm

Ribosomal RNA (rRNA) Binds to messenger RNA Uses the instructions from DNA to put amino acids in the correct order

Transfer RNA (tRNA) Delivers the amino acids to the ribosomes to be made into a protein

The Genetic Code nucleotide sequence transcribed from DNA to a strand of mRNA is a genetic message that has all the information needed to build a protein. The message is in a special language that uses nitrogenous bases as the alphabet.

proteins are made up of amino acid chains. There are 20 different amino acids. These amino acids are made from only four nitrogenous bases.

Each group of three nitrogenous bases is known as a codon. Ex: The codon for the amino acid alanine is G-C-U. The codon for lysine is A-A-A. Every amino acid has a three-letter codon In amino acid chain there is codons that tell mRNA when to start and when to stop.

Do Now: What is the differences between DNA and RNA?

In nucleus and cytoplasm DNA RNA (3 types) Sugar Deoxyribose Ribose Bases G, C, A, T G, C, A, U (uracil) Structure Double-stranded Single-stranded Location in a Cell Only in the nucleus In nucleus and cytoplasm Base Pairing C-G and A-T C-G and A-U

What is ……? Replication Transcription Translation protein formation CENTRAL DOGMA

Translation The process of changing the information in mRNA into an amino acid chain in protein is called translation.

1. The mRNA moves to the cytoplasm. 2. A ribosome (rRNA) attaches itself to the start codon, A-U-G, on the mRNA. 3. Transfer RNA (tRNA) molecules, carrying amino acids, approach the ribosome. The nitrogenous base sequence that is the complement to the mRNA sequence is the anticodon. If the mRNA codon is G-C-C, the tRNA anticodon is C-G-G. For every codon on mRNA there is an anticodon on tRNA. 4. The ribosome attaches the anticodon to the codon and the amino acids bond. The ribosome then slides to the next codon. 5. Again the ribosome attaches the anticodon to the codon, amino acids bond, and the ribosome slides over. 6. This translation process continues until the stop codon is reached. At this point the amino acids have formed a chain and when the stop codon is reached, the chain is released.

The 3 main types of RNA are ___, ___, & ___. 2. Copying part of a nucleotide sequence of DNA into a complementary sequence in RNA is called ____. 3. During the process of _____, the information carried by mRNA is used to produce proteins. 4. Each tRNA molecule contains 3 unpaired bases, called the _____, which ensure that amino acids are added in the correct sequence.

Do Now: What is mutation?

Mutations Any change in the sequence of DNA Can be caused by errors in: DNA replication Transcription Cell division External agents

Mutations in Reproductive Cells: Birth Defects Within the egg or sperm cells Can produce new traits Can result in proteins that do not work (can kill organism) Could have positive effects Faster Stronger Important in the evolution of a species

Mutations in Body Cells Not passed on to offspring May impair cell function Can affect genes that control cell division (cancer)

Radiation from the sun, X rays, or radioactive materials can change the DNA of skin, muscle, or bone cells. Since these cells are not sex cells, the changes in the DNA are not passed on to offspring. However, the organism may be harmed by the mutation. When mutated cells divide they pass on the mutation.

THE DOG BIT THE CAT THE DOG BIT THE CAR

Point Mutation Change in 1 N-base in DNA CGATTACGC (normal DNA) CGATTTCGC (mutated DNA)

THE DOG BIT THE CAT (correct) THE DOB ITT HEC AT (deleted base (G)) THE DOC GBI TTH ECA T (added base (C))

Frameshift Mutation 1 N-base is added or deleted Changes all codons from that point on May cause no problems or can be severe More dangerous than point mutations

Chromosomal Mutations Involve many genes Usually very bad

Homework : What are the Causes of Mutations? Can DNA be repaired?