Chapter 10: Biochemistry of The molds Genome

Hämmerling used _________, a single-celled alga, to demonstrate that genetic information is stored in the nucleus.

Acetabularia

Beadle and Tatum’s one gene–one enzyme hypothesis was derived from experiments with _________ spores.

mold

Griffith’s experiments showed transformation of Streptococcus cells by demonstrating that harmless bacteria could become _________.

deadly

Avery et al determined that _________ was the transforming factor in their experiments with Streptococcus pneumoniae.

DNA

Hershey and Chase used __________ to provide proof that DNA is the genetic material.

bacteriophages

Nucleotides consist of a phosphate group, a five-carbon sugar, and a __________ base.

nitrogenous

In DNA structure, the two strands are oriented in opposite directions; this is referred to as being __________.

antiparallel

RNA differs from DNA in that it contains __________ sugar instead of deoxyribose.

ribose

tRNA is responsible for bringing the appropriate __________ to the ribosome during protein synthesis.

amino acids

A __________ is a segment of DNA that contains the instructions for producing a specific protein or RNA molecule.

gene

Describe how Hämmerling used single-celled Algae to find that genetic information was located in the nucleus.

Hammerling used Acetubularia, a single-celled alga, to show that genetic information is stored in the nucleus. He cut off either the cap or food of the cells. When he removed the cap, it grew back, but when he took off the food, no new foot grew. This pointed to the food, which holds the nucleus, as the source of the genetic material. In other experiments, he switched the stalks between two different species and found that the cap shape was always determined by the foot’s nucleus, confirming that the nucleus controls the cell’s traits.

How did Beadle and Tatum’s experiments with mold spores result in their one gene-one enzyme hypothesis.

Beadle and Tatum’s experiments with mold spores led to the “one gene-one enzyme” hypothesis by showing how mutation is specific genes affected the mold’s ability to produce certain enzymes. They exposed Neurospora crassa spores to X-rays to cause mutations, then grew them on different types of media. Mutants that couldn’t grow on minimal medium (no amino acids) but could grow on complete medium (with added amino acids) were identified. By adding individual amino acids to the minimal medium, they found that each mutant was missing the ability to produce a specific enzyme in the Arginine Biosynthesis Pathway. This showed that each gene is responsible for making a specific enzyme, which led to their hypothesis that one gene encodes one enzyme. They also were able to group the mutants for Arg biosynthesis into 3 groups that could make Arg from precursors. They realized that each step in the biosynthesis must be catalyzed by different factors (what we now know are enzymes coded for by genes, and the mutations disrupted each gene separately).

How did the Griffith experiments show transformation of Streptococcus cells?

Griffith's experiments with Streptococcus pneumoniae demonstrated the process of transformation by showing how harmless bacteria could become deadly. He worked with two strains: the rough (R) strain, which is nonpathogenic and lacks a capsule, making its colonies appear rough on plates, and the smooth (S) strain, which is pathogenic and has a capsule that helps it evade the immune system. The capsule gives the S strain a smooth appearance on plates. In his experiments, Griffith injected mice with different combinations of these strains. When mice were injected with the live S strain, they died because the bacteria were virulent. Mice injected with either the live R strain or heat-killed S strain survived, as neither was harmful. However, when he injected mice with a mixture of live R strain and heat-killed S strain (neither killed the mice) , the mice died. From the dead mice, Griffith recovered only live S strain bacteria. This meant something from the dead, heat-killed S strain had been transferred to the live R strain, transforming it into the deadly S strain. He called this unknown factor the "transforming principle," which later helped scientists understand that DNA carries genetic information.

How did Avery et al determine that DNA, and not the other organic polymers, was the transforming factor?

Avery and his colleagues determined that DNA was the transforming factor through a series of experiments where they selectively destroyed different organic molecules in the heat-killed Streptococcus pneumoniae S strain. First, they extracted a mixture of organic materials, including proteins, lipids, carbohydrates, and nucleic acids, from the heat-killed S strain, which had been shown to transform the harmless R strain into the pathogenic S strain. They then treated the mixture with enzymes that specifically broke down one type of organic molecule at a time: protease for proteins, lipase for lipids, amylase for carbohydrates, ribonuclease (RNase) for RNA, and deoxyribonuclease (DNase) for DNA. After each treatment, they tested whether the remaining material could still transform the R strain. They found that destroying proteins, lipids, carbohydrates, or RNA did not stop the transformation, but when DNA was destroyed with DNase, the transformation did not occur. This led them to conclude that DNA was the "transforming factor" responsible for passing genetic information, proving that DNA, not other molecules, carries hereditary material. This suggested DNA was the transforming factor, but did not prove it because it was a loss of function result.

Describe Hershey and Chase’s experimental proof that DNA was the genetic material.

Hershey and Chase provided experimental proof that DNA is the genetic material through their work with bacteriophages, which are viruses that infect bacteria. In their classic experiment conducted in 1952, they prepared two batches of T2 phages. In the first batch, they labeled the DNA with radioactive phosphorus-32 (³²P), as DNA contains phosphorus but proteins do not. In the second batch, they labeled the proteins with radioactive sulfur-35 (³⁵S), since proteins contain sulfur but DNA does not. The labeled phages were then allowed to infect Escherichia coli (E. coli) bacteria. After the phages attached to the bacteria and injected their genetic material, the researchers used a blender to separate the phage protein coats from the bacterial cells. They then centrifuged the mixture to separate the heavier bacterial cells from the lighter phage coats, with the bacterial cells forming a pellet at the bottom and the remaining phage coats staying in the supernatant. Upon measuring the radioactivity in both the bacterial pellet and the supernatant, Hershey and Chase found that the radioactive phosphorus (³²P) was present in the bacterial pellet, indicating that DNA had entered the bacteria, while the radioactive sulfur (³⁵S) remained in the supernatant, showing that the protein did not enter the cells. This clear distinction demonstrated that DNA, not protein, was the genetic material responsible for carrying the instructions for producing new phages, providing strong evidence that DNA is the hereditary material and advancing the understanding of genetics.

Describe the structure of nucleotide monomers

Each nucleotide consists of three components: a phosphate group, a five-carbon sugar (ribose in RNA and deoxyribose in DNA), and a nitrogenous base (adenine, thymine, cytosine, or guanine in DNA; adenine, uracil, cytosine, or guanine in RNA).

Describe the structure of nucleotide polymers.

In nucleic acid polymers, nucleotides are linked together by phosphodiester bonds, which form between the phosphate group of one nucleotide and the sugar of the next. This creates a sugar-phosphate backbone with nitrogenous bases extending from it. The sequence of these bases encodes genetic information.

How is DNA complementary?

DNA is composed of two strands that run in opposite directions, making them antiparallel. One strand runs in a 5' to 3' direction. 

How is DNA antiparallel?

DNA is composed of two strands that run in opposite directions, making them antiparallel. One strand runs in a 5' to 3' direction.

Describe the similarities between RNA and DNA

Both RNA and DNA are nucleic acids made up of nucleotide monomers. They both play crucial roles in storing and expressing genetic information. Each contains the bases adenine, cytosine, and guanine with a sugar-phosphate backbone.

Describe the differences between RNA and DNA

RNA contains ribose sugar, while DNA contains deoxyribose sugar (which lacks one oxygen atom on the 2' carbon of the sugar - this makes DNA more stable than RNA).). DNA is typically double-stranded, forming a double helix, while RNA is usually single-stranded. DNA has thymine (T), whereas RNA has uracil (U) in place of thymine. DNA primarily serves as the genetic blueprint; DNA stores information for cell function and is passed to daughter cells through vertical gene transfer during replication. A cell duplicates its DNA before dividing, ensuring each new cell gets a copy. DNA can also be broken down for nucleosides and nucleotides but does not serve a structural role. RNA is involved in various functions related to protein synthesis (mRNA, rRNA, tRNA,) and gene expression.

Identify functions for various RNAs used in protein synthesis: mRNA

mRNA carries the genetic information from DNA to the ribosome, where proteins are synthesized. It serves as a template for translating the sequence of nucleotides into an amino acid sequence.

Identify functions for various RNAs used in protein synthesis: tRNA

tRNA is responsible for bringing the appropriate amino acids to the ribosome during protein synthesis. Each tRNA molecule is specific to one amino acid and has an anticodon that pairs with the corresponding condon on the mRNA.

Identify functions for various RNAs used in protein synthesis: rRNA

rRNA is a key component of ribosomes, the cellular machinery where proteins synthesis occurs. It helps catalyze the formation peptide bonds between amino acids and ensures the proper alignment of mRNA and tRNA during translation.

Define gene

Gene is a segment of DNA that contains the instructions for producing a specific protein or RNA molecules, influencing an organism’s traits and functions. AKA stretch of DNA that codes for a functional product.

Define chromosome

Tightly coiled structure made of DNA and proteins that carries genetic information. Chromosomes are found in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells.

Define genome

The complete set of genetic material, including all of the organism’s genes and non-coding sequences, contained within its chromosomes. It represents the full hereditary information of an organism. AKA all genetic info in cells. This can also include viruses in the cells, and also the chromosomes of the mitochondria and/or chloroplasts.

Define Plasmid

A plasmid is a small, circular piece of DNA that is separate from chromosomal DNA and can replicate independently. Plasmids are commonly found in bacteria and often carry genes that confer advantageous traits, such as antibiotic resistance.

Genotype:

The genetic makeup of an organism, specifically the versions of a gene it possesses. It represents the information encoded in the DNA.

Phenotype:

The physical traits that can be seen and biochemical characteristics of an organism, resulting from the interaction between its genotype and the environment.

Describe the prokaryotic chromosome structure and packaging

Have a single, circular chromosomes located in the nucleoid region. This chromosome is not associated with histones and is relatively simple in structure. The chromosome is tightly coiled to fit within the cell. DNA-binding proteins help organize the DNA within the nucleoid.

Describe the Eukaryotic chromosome structure and packaging

Have multiple linear chromosomes located within a membrane-bound nucleus. Are complex and consist of DNA tightly coiled around histone proteins, Forming a chromatin structure. Including plasmids, mitochondria/chloroplast, and viruses.