GE 345: Week 1

V. DNA -- Master Controller

    Physiology/Kinesiology

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Updated by Tracey 8 July 02

Overview | Gross Cell | Cell Structure | Cell Innards | Synthesis

DNA (deoxyribonucleic acid) controls cell reproduction and function by determining the substances synthesized within the cell, such as structures, enzymes and chemicals. DNA controls RNA formation, which in turn controls protein formation. These proteins can be structural or enzymes.

Basic DNA Structure

Double-helical strands of DNA composed of simple chemical compounds bound together. The chemical base consists of phosphoric acid bound to deoxyribose sugar and one of 4 nitrogenous bases.

Nucleotide: one molecule each of phosphoric acid, deoxyribose and one of the four bases form deoxyadenylic, deoxythymidylic, deoxyguanylic or deoxycytidylic acid. Bound to matching nucleotide on he opposite strand via a loose hydrogen bond between the bases. Adenine always bonds with thymine, guanine always bonds with cytosine.

Nitrogenous Base Classes and Pairs

DNA controls substance formation by means of a genetic code, consisting of successive base triplets. Each group of three successive bases is a code word and successive triplets control the sequence of amino acids synthesized in a protein molecule. Triplets are generally "read" along one strand of the helix.

Transcription

Process by which DNA in the nucleus controls cell functions in the cytoplasm by controlling formation of RNA (ribonucleic acid). The genetic "code" is transferred to the RNA in a process called transcription.

RNA composed of sugar ribose instead of deoxyribose. Thymine is replaced by another pyrimidine, uracil.

RNA Synthesis:

• DNA strands temporarily separate.
• One strand used as template for synthesis of RNA molecules
• RNA forms complementary code triplets to those in DNA (codons)
• Codons control amino acid sequences in proteins synthesized later in the cytoplam

Complementary RNA Bases:

RNA codon base triplets. Control amino acid development. More than one codon can create an amino acid, as shown in the following table:

RNA Types

• Messenger RNA: contain the complementary codons to the DNA code triplets. The codons direct the synthesis of amino acids (protein molecules).
• Transfer RNA: acts as a carrier to transport a specific type of aa to the appropriate place in the newly forming protein molecule in the ribosomes.
• Ribosomal RNA: makes up 60 percent of the ribosome (the rest being structural proteins and enzymes). The ribosome reads mRNA codons to form the protein molecules before releasing it into the cytoplasm.

Many protein molecules attach to receptors in the endoplasmic reticulum, carrying the ribosome along with them, thereby creating a "granular" appearance to areas of the ER where proteins are being formed.

DNA Control of Cell Biochemistry

A sequence of genes called an operon controls formation of enzymes needed for specific cell proceses. Sructural genes are responsible for forming the respective enzymes. Operons can be activated or repressed based on the cell's needs, usually by regulatory proteins.

Cell reproduction begins with replication of the entire DNA so there is a complete DNA set for each daughter cell.

Overview | Gross Cell | Cell Structure | Cell Innards | Synthesis