Chapter1 Diversity and Universality of Organisms

Chapter2 Replication of Genetic Information

Chapter3 Expression of Genes

Chapter 4 Regulation of Gene Expression

Chapter 5 Cell Membrane Structure and Organelles

Chapter 6 Cytoskeleton

Chapter 7 Metabolism

Chapter8 Energy

Chapte9 Signal Transduction and Cell Growth

Chapte10 Development and Differentiation

Chapte11 Intercellular Communication and Tissue Architecture

Chapte12 Reproduction and Meiosis

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3Problems

 

 

Briefly explain the characteristics shared and not shared by the processes of replication and transcription.

 

 

Using the terms below, briefly outline how the genetic information of genomic DNA is eventually converted to proteins:
Codon, messenger RNA (mRNA), amino acid, aminoacyl-tRNA (AA-tRNA), nucleus, cytoplasm, ribosome

 

 

Briefly outline the process that occurs during mRNA synthesis in eukaryotes between the transcription and completion of mRNA.

In humans, one chromosomal genome set is inherited from each of the mother and father.

1)

Consider a case in which a DNA sequence inherited from a parent has a mutation, resulting in illness. If a disease manifests itself as a phenotype only when mutation occurs in both copies of a gene derived from both the mother and father, is it a dominant or recessive hereditary disease?

2)

For the scenario in 1), it is assumed that the mutation occurs at a site that encodes an amino acid. What kind of mutation is generally considered to occur in this case?

3)

If a disease manifests itself as a phenotype when a mutation occurs in one of the two copies of a gene (derived from either the mother or the father), is it a dominant or recessive hereditary disease?

4)

For the scenario in 3), it is assumed that the mutation occurs at a site that encodes an amino acid. What kind of mutation is generally considered to occur in this case?

 

 

Briefly explain the characteristics shared and not shared by the processes of replication and transcription.

Shared mechanisms: Both replication and transcription require a template, and macromolecules are synthesized through the insertion of complementary nucleotides to the template sequence. In replication and transcription, synthesis starts from 5’ and proceeds toward 3’ - the direction opposite to the template. In both replication and transcription, nucleoside 5'-triphosphates are used as materials, and pyrophosphates are released.
Unshared mechanisms: In replication, daughter strands are synthesized using whole parent DNA strands; however, in transcription, only genes (including their adjacent regions), rather than the whole DNA strand, are transcribed. In replication, daughter strands are synthesized using both parent strands as templates, whereas in transcription, RNA strands are synthesized from genes using only one strand (the sense strand) as a template. Replication requires RNA primers, and transcription does not.

 

 

Using the terms below, briefly outline how the genetic information of genomic DNA is eventually converted to proteins:
Codon, messenger RNA (mRNA), amino acid, aminoacyl-tRNA (AA-tRNA), nucleus, cytoplasm, ribosome

RNA synthetase binds to the promoter of a gene for mRNA synthesis. In prokaryotes, a ribosome binds to mRNA that is still being synthesized and produces a protein. In eukaryotes, pre-mRNA is first synthesized in the nucleus and, after undergoing processing and becoming mRNA, is transported through the nuclear pores into the cytoplasm, where it binds to ribosomes for protein synthesis. Amino acids bind to tRNA through the action of aminoacyl-tRNA synthetase - an enzyme unique to each amino acid type - thus becoming aminoacyl-tRNA. Three nucleotides of mRNA (a codon) designate one amino acid, and a codon on mRNA determines an amino acid through the formation of a base pair between a codon on mRNA and an anticodon on tRNA. mRNA is thus bound with aminoacyl-tRNA on the surface of ribosomes, after which the connections between tRNA and amino acids are cut, thereby forming peptide bonds of amino acids and elongating peptide chains.

 

 

Briefly outline the process that occurs during mRNA synthesis in eukaryotes between the transcription and completion of mRNA.

In eukaryotes, pre-mRNA (precursor mRNA) is transcribed from DNA, and undergoes processing (such as capping, splicing and poly-A insertion) to become mRNA. In capping, the 5’ end of pre-mRNA and 7-methylguanosine form a 5’-5’ bond via three phosphates. When protein synthesis is initiated, proteins that recognize and bind to the cap structure act to join mRNA and ribosomes together. Splicing is a process in which introns are removed from pre-mRNA and only exons are connected. Different mRNA molecules can be produced from the same pre-mRNA through alternative splicing, meaning that different proteins may result from the same gene.
In poly-A addition, pre-mRNA is cut downstream of the poly-A signal sequence (often AAUAAA), and poly-A is added there. Poly-A is involved in the initiation of protein synthesis and the suppression of mRNA degradation. See Fig. 3-8.

In humans, one chromosomal genome set is inherited from each of the mother and father.

1)

Consider a case in which a DNA sequence inherited from a parent has a mutation, resulting in illness. If a disease manifests itself as a phenotype only when mutation occurs in both copies of a gene derived from both the mother and father, is it a dominant or recessive hereditary disease?

A recessive hereditary disease

2)

For the scenario in 1), it is assumed that the mutation occurs at a site that encodes an amino acid. What kind of mutation is generally considered to occur in this case?

Generally, in cases where a termination codon is inserted in a region that encodes amino acids, thus causing the production of an incomplete protein (the loss-of-function mutation), recessive hereditary diseases may result. This is because, in such mutations, if the other copy of the gene derived from a parent is normal, the normal copy often makes up for the mutated one. It has also become increasingly clear from recent research that if unnecessary termination codons are inserted in an exon, the mRNA transcribed from it is immediately degraded and not translated.

3)

If a disease manifests itself as a phenotype when a mutation occurs in one of the two copies of a gene (derived from either the mother or the father), is it a dominant or recessive hereditary disease?

A dominant hereditary disease

4)

For the scenario in 3), it is assumed that the mutation occurs at a site that encodes an amino acid. What kind of mutation is generally considered to occur in this case?

In cases where base substitution results in amino acid mutation that adds new functions to a protein (the gain-of-function mutation), dominant hereditary diseases may result. Amino acid mutations caused by base substitution are called missense mutations, and those in which termination codons are inserted, for example, are called nonsense mutations.

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