Mrs. Degl

Molecular Genetics

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus, but a small amount of DNA can also be found in the mitochondria.

Genes are sections of DNA molecules. DNA controls the cellular activities by controlling the production of enzymes.

Mrs. Degl

DNA molecules are very large and each is made up of thousands of repeating units called nucleotides.

A DNA nucleotide is composed of three parts:1. A Phosphate Group2. One 5 carbon sugar molecule, called Deoxyribose3. One Nitrogenous Base

Nucleotides

Mrs. Degl

Nitrogenous Bases There are 4 different nitrogenous

bases:

1.Adenine2.Cytosine3.Guanine4.Thymine

Therefore, there are 4 different types of nucleotides, depending on which nitrogenous base is present.

Mrs. Degl

Watson & Crick Model of DNA

In 1953, James Watson and Francis Crick developed a model of the DNA Molecule. They based their model on their own knowledge and the knowledge of other scientists who were looking into “The Secret of Life”.

•The DNA molecule consists of two long chains of nucleotides attached in a ladder like fashion. • The sides of the ladder are the alternating phosphate and deoxyribose molecules. •The inside of the ladder consists of pairs of nitrogenous bases bonded together by hydrogen bonds.

Mrs. Degl

The two chains are twisted together into a spiral, called a Double Helix.

Mrs. Degl

The four bases bond together in only one way:

Adenine pairs with Thymine

Guanine pairs with Cytosine

Because the two strands bond together in only one way, the two strands are always complementary. If you know the order of the bases on one strand, then you know the order on the other strand.

Mrs. Degl

DNA Replication

DNA can make exact copies of itself. This is called replication. This happens in Mitosis and Meiosis.

•In replication, the double stranded helix unwinds, which is called unzipping. For this to happen, the bonds holding the nitrogen bases together have to break.•Free nucleotides from the cytoplasm now enter the nucleus and bond to their complementary base on the DNA strand.•Replication produces 2 copies that are identical to the original DNA molecule.•Special enzymes carry out this procedure.

Mrs. Degl

RNA• RNA is ribonucleic acid• The 5 carbon sugar is ribose,

instead of deoxyribose• The nitrogenous base is

Uracil, instead of Thymine• RNA is only one strand, not

a double helix.

There are 3 types of RNA:1. mRNA (messenger)2. tRNA (transfer)3. rRNA (ribosomal)

Mrs. Degl

Mrs. Degl

mRNA•mRNA is synthesized in the nucleus.•A genetic code contains the information for the sequence of amino acids in a particular protein.

•This code is present in mRNA molecules and is three bases long, and is specific. This sequence is known as a codon.

Mrs. Degl

tRNA

•tRNA are found the cytoplasm.•They carry amino acid molecules to the ribosomes, which are the sited for protein synthesis.•Ribosomes are made of rRNA and proteins.•There are 20 different kids of amino acids in cells, and there is a different form of tRNA for each amino acid.•Each kind of tRNA has a 3 nucleotide sequence, called an anticodon, which is complementary to a codon on the mRNA.

Mrs. Degl

The synthesis of proteins takes two steps: transcription and translation. Transcription takes the information encoded in DNA and encodes it into mRNA, which heads out of the cell’s nucleus and into the cytoplasm, attached to tRNA. During translation, the mRNA works with a ribosome and tRNA to synthesize proteins. The resulting chain of amino acids is a polypeptide. The polypeptide can either be one chain or many chains.                                                                                                                                                       

Protein Synthesis