CH17

Explain how DNA and RNA molecules have structural similarities and differences that define function.

DNA is made of two strands, connected by hydrogen bonds. Each strand is made of nucleotides. A nucleotide consists of one of four different nitrogenous bases (adenine, cytosine, guanine or thymine), a 5-carbon sugar (deoxyribose) and a phosphate group. RNA is made of a single strand, similar to those of DNA.

Explain how genetic information flows from a sequence of nucleotides in a gene to a sequence of amino acids in a protein.

During the process of transcription, the information stored in a gene's DNA is transferred to a similar molecule called RNA (ribonucleic acid) in the cell nucleus. Both RNA and DNA are made up of a chain of nucleotide bases, but they have slightly different chemical properties. The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm. Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a specialized complex called a ribosome, which "reads" the sequence of mRNA bases. Each sequence of three bases, called a codon, usually codes for one particular amino acid. (Amino acids are the building blocks of proteins.) A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. Protein assembly continues until the ribosome encounters a "stop" codon (a sequence of three bases that does not code for an amino acid).

Compare where transcription and translation occur in prokaryotes and in eukaryotes.

In a prokaryotic cell, transcription and translation are coupled; that is, translation begins while the mRNA is still being synthesized. In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm.

Explain how genetic engineering techniques can manipulate the heritable information of DNA and, in special cases, RNA.

Phenotypes are determined through protein activities. Examples of protein activities include enzymatic reactions, transport by proteins, synthesis, and degradation. Genetic engineering techniques can manipulate the heritable information of DNA and, in special cases, RNA. Examples genetic engineering techniquest include electrophoresis, plasmid-based transformation, restriction enzyme analysis of DNA and polymerase chain reaction

Describe how phenotypes are determined through protein activities.

Some proteins serve structural functions (for example, in the maintenance of cell and/or tissue shape and rigidity) while others are involved in the transport of molecules and communication between cells. A substantial proportion of proteins are enzymes , catalyzing chemical reactions for the synthesis and transformation of virtually all biological molecules. The varying types and quantities of all biological molecules in the cells and tissues of an individual is what ultimately leads to phenotypic variation.

Predict how a change in a specific DNA or RNA sequence can result in changes in gene expression.

The pattern of base pairs in the DNA double helix encodes the instructions for building the proteins necessary to construct an entire organism. DNA, or deoxyribonucleic acid, is found within most cells of an organism, and most organisms have their own unique DNA code.

Distinguish between transcription and translation.

Transcription is the synthesis of RNA from a DNA template where the code in the DNA is converted into a complementary RNA code. Translation is the synthesis of a protein from an mRNA template where the code in the mRNA is converted into an amino acid sequence in a protein.

Describe how genetic information is translated into polypeptides.

Translation is the process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids in a polypeptide chain Ribosomes bind to mRNA in the cell's cytoplasm and move along the mRNA molecule in a 5' - 3' direction until it reaches a start codon (AUG) Anticodons on tRNA molecules align opposite appropriate codons according to complementary base pairing (e.g. UAC will align with AUG) Each tRNA molecule carries a specific amino acid (according to the genetic code) Ribosomes catalyse the formation of peptide bonds between adjacent amino acids (via a condensation reaction) The ribosome moves along the mRNA molecule synthesising a polypeptide chain until it reaches a stop codon, at this point translation stops and the polypeptide chain is released