High School Biology : Understanding Gene Coding

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #1 : Understanding Gene Coding

The central dogma of molecular biology is the method by which cells transfer nucleic acids into functional molecules. Which of the following depicts the central dogma of molecular biology?

Possible Answers:

Correct answer:

Explanation:

The central dogma of molecular biology states that DNA is transcribed into RNA, which is then translated into protein.

Example Question #2 : Understanding Gene Coding

A mutation occurs, changing the DNA sequence but leaving the final amino acid sequence unaltered. How is it possible that the underlying DNA sequence is different but the amino acid sequence remains the same?

Possible Answers:

Cells with mutated genomes will undergo apoptosis

The genome encodes for "degenerate codons," indicating that more than one codon can encode for a particular amino acid

The cell has a specific memory that corrects the DNA sequence before transcription

DNA checkpoints do not allow the cell to transcribe mutated genes

Correct answer:

The genome encodes for "degenerate codons," indicating that more than one codon can encode for a particular amino acid

Explanation:

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.

Example Question #3 : Genes And Dna

What term describes the section of DNA that codes for a single protein?

Possible Answers:

Allele

Locus

Gene

Genotype

Correct answer:

Gene

Explanation:

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.

Example Question #3 : Understanding Gene Coding

The first cross done between two individual parents is called the "Parental generation," or "P generation." What are the next two generations normally called?

Possible Answers:

G1 and G2

F1 and G1

F1 and F2

P1 and P2

Correct answer:

F1 and F2

Explanation:

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.

Example Question #4 : Understanding Gene Coding

What is the definition of an allele?

Possible Answers:

A section of DNA that codes for a gene product

A location of a protein

A different version of the same gene, or group of genes

A portion of unreplicated DNA

Correct answer:

A different version of the same gene, or group of genes

Explanation:

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.

Example Question #122 : Genetics And Evolution

In eukaryotic organisms, a DNA sequence of 10,000 nucleotides codes for a protein that is only 300 amino acids long. What is the best explanation of this phenomenon? 

Possible Answers:

Three nucleotides correspond with one amino acid

Certain nucleotides are skipped when the mRNA sequence is transcribed

The gene is a mutation

The entire seqeunce is translated, and the cell cleaves the amino acid chain so that the desired protein remains

Eukaryotic DNA is comprised of coding and non-coding strands

Correct answer:

Eukaryotic DNA is comprised of coding and non-coding strands

Explanation:

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. 

Example Question #4 : Genes And Dna

What defines the reading frame of a messenger RNA (mRNA)?

Possible Answers:

A promoter

Presence of start codon

The ribosome binding site

A RNA polymerase binding site

Correct answer:

Presence of start codon

Explanation:

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

Example Question #8 : Genes And Dna

An individual having green eyes or being tall are examples of which of the following?

Possible Answers:

None of these

Phenotype

Genotype 

Heritable genetic identity

Correct answer:

Phenotype

Explanation:

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. 

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