Chapter 17: Nucleic Acids and Protein Synthesis

DNA

RNA

Two Main Nucleic Acids

Nucleotides

These are the repeating monomer units.

pyrimidine / purine

The nitrogen-containing bases in nucleic acids are derivatives of _.

Adenine

Guanine

The purine bases with double rings are what?

Cytosine

Thymine

The pyrimidine bases with double rings are what?

uracil

RNA contains the same pyrimidine and purine bases as DNA, except thymine (T) is replaced by _.

Ribose

The five-carbon sugar in RNA which gives the letter R in the abbreviation of RNA.

Deoxyribose

The five-carbon sugar in DNA, is similar to ribose except that there is no hydroxyl group.

Nucleosides

A combination of sugar and a base, is produced when the nitrogen atom in a pyrimidine or a purine base forms an N-glycosidic bond to carbon 1 of a sugar, either ribose or deoxyribose.

Nucleotides

These are nucleosides in which a phosphate group bonds to the —OH group on carbon 5 of ribose or deoxyribose.

Nucleic Acids

These are polymers of many nucleotides in which the 3′-hydroxyl group of the sugar in one nucleotide bonds to the phosphate group on the 5′-carbon atom in the sugar of the next nucleotide.

Phosphodiester bond

The link between the sugars in adjacent nucleotides.

Primary Structure of Nucleic Acid

It is this sequence of bases that carries the genetic information from one cell to the next.

double helix

In 1953, James Watson and Francis Crick proposed that DNA was a that consisted of two polynucleotide strands winding about each other like a spiral staircase.

James Watson and Francis Crick

In 1953, they proposed that DNA was a double helix that consisted of two polynucleotide strands winding about each other like a spiral staircase.

Complementary Base Pairs

The pairs AT and GC; are the specific pairing of the bases occurs because adenine and thymine form only two hydrogen bonds, while cytosine and guanine form three hydrogen bonds.

DNA Replication

This process begins when helicase catalyzes the unwinding of a portion of the double helix by breaking the hydrogen bonds between the complementary bases.

RNA

It makes up most of the nucleic acid found in the cell, is involved with transmitting the genetic information needed to operate the cell.

Ribosomal RNA (rRNA)

• The most abundant type of RNA is combined with proteins to form ribosomes.
• Ribosomes, which are the sites for protein synthesis, consist of two subunits: a large subunit and a small subunit.

Messenger RNA (mRNA)

It carries genetic information from the DNA, located in the nucleus of the cell, to the ribosomes located in the cytoplasm.

Transfer RNA (tRNA)

The smallest of the RNA molecules interprets the genetic information in mRNA and brings specific amino acids to the ribosome for protein synthesis.

Anticodon

A series of three bases that complements three bases on mRNA.

Transcription

Genetic information for the synthesis of a protein is copied from a gene in DNA to make mRNA.

Translation

tRNA molecules convert the information in the mRNA into amino acids, which are placed in the proper sequence to synthesize a protein.

Genetic Code

It consists of a series of three nucleotides in mRNA called codons that specify the amino acids and their sequence in the protein.

Protein Synthesis

• Once the mRNA is synthesized, it migrates out of the nucleus into the cytoplasm to the ribosomes.
• In the translation process, tRNA molecules, amino acids, and enzymes convert the codons on mRNA to build a protein.

Activation

_ of tRNA occurs when aminoacyl–tRNA synthetase forms an ester bond between the carboxylate group of its amino acid and the hydroxyl group on the acceptor stem.

Translocation

The initial tRNA detaches from the ribosome, which shifts to the next available codon.

start codon

The first codon in mRNA is a , AUG, which forms hydrogen bonds with methionine–tRNA.

methionine

Another tRNA hydrogen bonds to the next codon, placing a second amino acid adjacent to .

peptide

A ____ bond forms between the C-terminal of methionine and the N-terminal of the second amino acid

chain elongation,

During _. the ribosome moves along the mRNA from codon to codon, so that the tRNAs can attach new amino acids to the growing protein chain.

polysome

Sometimes, translates the same strand of mRNA to produce several copies of the protein at the same time.

Stop codons

____ are encountered which the termination of protein synthesis and the release of the protein chain from the ribosome.

Mutation

A change in the nucleotide sequence of DNA.

somatic cell

If a mutation occurs in a , the altered DNA will be limited to that cell and its daughter cells.

cancer

If the mutation causes uncontrolled growth, _ could result.

germ cell

If a mutation occurs in a ____, then all the DNA produced in a new individual will contain the same genetic change.

genetic disease

When a mutation severely alters the function of structural proteins or enzymes, the new cells may not survive or the person may exhibit a _.

Point Mutation

The replacement of one base in the template strand of DNA with another.

Silent Mutation

This occurs if a substitution gives a codon for the same amino acid, and there is no change in the amino acid sequence in the protein.

Frameshift Mutation

A base is inserted into or deleted from the normal order of bases in the template strand of DNA.

Genetic Disease

It is the result of a defective enzyme caused by a mutation in its genetic code.

Galactosemia

The transferase enzyme required for the metabolism of galactose-1-phosphate is absent, resulting in the accumulation of galactose-1-phosphate, which leads to cataracts and mental retardation.

Cystic fibrosis

• It is caused by a mutation in the gene for the protein that regulates the production of stomach fluids and mucus
• It is one of the most common inherited diseases in children, in which thick mucus secretions make breathing difficult and block pancreatic function.

Down syndrome

It is the leading cause of mental retardation, occurring in about 1 of every 800 live births; the mother’s age strongly influences its occurrence.

Familial hypercholesterolemia

It occurs when there is a mutation of a gene on chromosome 19, which produces high cholesterol levels that lead to early coronary heart disease in people 30 to 40 years old

Muscular dystrophy

• It is caused by a mutation in the X chromosome.
  • This muscle-destroying disease appears at about age 5, with death by age 20, and occurs in about 1 of 10 000 males.

Huntington’s disease

• It affects the nervous system, leading to total physical impairment.
  • It is the result of a mutation in a gene on chromosome 4, which can now be mapped to test people in families with a history of HD.

Sickle-cell anemia

• It is caused by a defective form of hemoglobin resulting from a mutation in a gene on chromosome 11.
  • It decreases the oxygen-carrying ability of red blood cells, which take on a sickled shape, causing anemia and plugged capillaries from red blood cell aggregation.

Hemophilia

• It is the result of one or more defective blood-clotting factors that lead to poor coagulation, excessive bleeding, and internal hemorrhages.

Tay–Sachs disease

• It is the result of defective hexosaminidase A, which causes an accumulation of gangliosides and leads to mental retardation, loss of motor control, and early death.

Viruses

• These are small particles of 3 to 200 genes that cannot replicate without a host cell
• It does not have the necessary material such as nucleotides and enzymes to make proteins and grow.

Viral Infection

• It begins when an enzyme in the protein coat of the virus makes a hole in the host cell, allowing the viral nucleic acids to enter and mix with the materials in the host cell.

Reverse Transcription

It is a process that occurs once inside the host cell, it must first make viral DNA.

Retrovirus

A virus that contains RNA as its genetic material.

Reverse transcriptase

An polymerase enzyme in a retrovirus that uses the viral RNA template to synthesize complementary strands of DNA.

Provirus

A newly formed DNA that integrates with the DNA of the host cell.

HIV-1 Virus

Known to be the AIDS-causing agent.

HIV

A retrovirus that infects and destroys T4 lymphocyte cells, which are involved in the immune response.

saquinavir, indinavir, fosamprenavir, nelfinavir, ritonavir

Treatment of AIDS often combines reverse transcriptase inhibitors with protease inhibitors such as ____.

acquired immunodeficiency syndrome

AIDS

HIV

human immunodeficiency virus