Genes and DNA - High School Biology

The human genome can code for 64 different codons, but only produces 20 different amino acids. This results in some amino acids having multiple codes in order to use the remaining 44 available codons.

This ability of a single amino acid to have more than one possible codon is called "degeneracy." Occasionally when DNA is mutated, it will results in a codon that encodes the same amino acid. For example, a mutation from CUU in the mRNA sequence to CUG will still code for leucine.

A gene codes for a certain protein product, which is often associated with a certain trait. Each gene is found at a specific location, or locus, on a chromosome.

Alleles refer to different forms of DNA that can appear at the same locus. In other words, an allele is an alternative form of a given gene. Different alleles often result in different phenotypes, such as changes in color or size.

DNA nucleotides are organized to form codes. When DNA is transcribed into RNA, these codes are read by the ribosomes to create proteins. Each gene refers to a sequence of DNA that codes for a specific protein. Mutation to a specific gene will affect that protein coded for by that sequence.

A locus is the location of a gene on a chromosome, and an allele is an alternative form of a given gene. A genotype is the description of the alleles for a specific set of genes.

Following the P generation is the 1st offspring generation, called F1. When the F1 generation is crossed, the result is the 2nd offspring generation, called F2.

G1 and G2 actually refer to periods of growth during the cell cycle, and are not related to genetics and inheritance.

Eukaryotes possess coding (exon) and non-coding (intron) seqeunces that allow for incredibly long DNA sequences to correspond with relatively short peptides. Only the exons are translated after the mRNA sequence, which is transcribed fully from the DNA, undergoes mRNA splicing. Furthermore, while a codon (three nucleoties) does correspond with one amino acid, it does not account for the dramatic difference stated in the question. Also, the cell does not translate an entire unmodified mRNA sequence and cleave afterwards as that would be incredibly wasteful and potentially harmful to the cell.

The reading frame of a mRNA is established by AUG (start codon) which codes for methionine.

A phenotype refers to the observable traits within an individual such as eye color, adult height, weight, and skin color. The genetic contribution to a phenotype is referred to as genotype. Some phonotypical traits are determined by the genotype, while others are shaped by environmental factors.

A repressor is a transcription factor that negatively regulates expression of a target gene. An activator is a transcription factor that enhances expression of a target gene. Activators and repressors often bind to the same genomic sequence to precisely regulate transcription.

An inhibitor is a factor that modulates a biological or chemical process, such as a cell signaling pathway or an enzymatic reaction, but does not generally bind directly to DNA. An insulator is a protein that forms boundaries between active and inactive genomic regions, but generally does not have a direct effect on a target gene.

This is simply a matter of vocabulary. Introns do not contain coding sequences, while exons do. "Intron" comes from the word "intragenic," meaning between genes, and therefore between exons. During post-transcriptional modification, introns are spliced out of the initial RNA transcript.

The ribosome is where translation happens, but it requires both mRNA and tRNA. mRNA provides the "recipe" for the order of the amino acids in its codons, each of which corresponds to a specific amino acid in the chain, and the tRNA molecules come in and bind appropriately when their anti-codons are complementary to the mRNA codons. tRNA molecules carry the amino acids to the ribosome, where the actual protein chain is then synthesized.

The correct answer is operon. Found in prokaryotes and a few eukaryotes, operons allow transcription and translation of all the genes downstream of a promoter simultaneously. This is advantageous because these organisms are able to express a subset of related genes rapidly in response to external or internal stimuli.

Transcription factors are proteins that bind to the regulator region of genes in eukaryotes and regulate whether a gene is expressed or not. A TATA-box binding protein is recruited after the transcription factors bind to the regulator region, and it eventually recruits RNA polymease. Tyrosine recombinases are not involved in initating eukaryotic gene expression.

Plasmids are small pieces of DNA that are not part of a bacteria's genome. The genes contained on plasmids are not necessary for proper function of the bacteria. However, bacterial plasmids can carry genes to confer antibiotic resistance, and commonly do. Plasmids can be transferred between bacteria via conjugation, and can be integrated into their genomic DNA.. Plasmids are usually present in more than one copy per cell.

Bacteria organize some of their genes into operons. Operons contain genes of a similar function grouped together, and these genes are all transcribed together. For example, the lac operon involves the three genes required for breaking down lactose. There is no point in only transcribing one or two of the three genes since they are all required to break down lactose. Thus, they are under the control of a single operator and are all transcribed when the operator is active.

The correct answer is that prokaryotes only have exons, whereas eukaryotes have exons and introns. As a result, in eukaryotes, when mRNA is transcribed from DNA, the introns have to be cut out of the newly synthesized mRNA strand. The exons, or coding sequences, are then joined together. Prokaryotes do not have to process their mRNA to this extent.

The correct answer is operator. In most operons, repressors bind operators to prevent transcription of downstream genes.

Promoters are sequences of DNA upstream of genes that usually promote transcription by recruiting polymerases and other transcription factors. Enhancers are distant DNA sequences that promote transcription, whereas exons are the coding segments of a gene.

The correct answer is transcribe RNA from a DNA template. RNA polymerases are DNA-dependent, meaning that they require a DNA template; however, the new daughter strand that they create is composed of RNA. This RNA will then be translated into a functional protein by prokaryotic ribosomes.

Rho attaches to a Rho recognition site on the mRNA strand and uses ATP to move along the mRNA strand towards RNA polymerase. When RNA polymerase pauses at the terminator, Rho unwinds the DNA-RNA hybrid. RNA polymerase, Rho, and the newly synthesized mRNA are released.

Restriction Endonucleases, or otherwise known as restriction enzymes, allows biologist to “cut and paste” different DNA sequences together. The use of restriction endonucleases is critical for the creation of recombinant plasmids. Viral vectors is incorrect, as viral vectors are useful in the application of recombinant DNA plasmids, delivery to host cell, but not in forming.