Molecular Genetics (Chapter 18) - Unit 6

Question 1

What was Miesher’s contribution to the study of hereditary material?

Answer 1

• He contributed the term” nucleic acid” to describe a weakly acidic, phosphorus - containing substance that he had isolated from the nuclei of white blood cells.
• Scientist established the connection between nuclei acid and Mendel’s factory of inheritance.

Question 2

What conclusion did Avery, Macleod, and McCarthy draw from their study of the transforming principle?

Answer 2

• When they treated heat-killed pathogenic bacteria with a protein- destroying enzyme, transformation skill occurred.
• When they heat-killed pathogenic bacteria with a DNA destroying enzyme, transformation fit not occur.

Question 3

What conclusion did Hershey and Chase draw from the study of transforming principle?

Answer 3

Hershey and Chase used a strain of virus known as T2 bacteriophage, which consists of a protein coat surrounding a length of DNA.

Hershey and Chase concluded that protein was not genetic material, and that DNA was genetic material. Unlike Avery’s experiments on bacterial transformations, the Hershey-Chase experiments were more widely and immediately accepted among scientists.

Question 4

What was the contribution of each of the following researchers?

1. Chargaff
2. Franklin
3. Watson and Crick

Answer 4

• Chargaff - found that the amount of Adenine in Amy sample of DNA is alway approximately equal to the amount of thymine, and the amount of cytosine is alway approximately equal to the amount of guanine - this relationship became known as Chargaff’s rule.
• Franklin - observation provided crucial new information about the molecular structure of DNA. She was able to conclude that DNA has a helical structure with two regularly repeating patterns - one recurring at intervals of 0.34 nm, and the other recurring at intervals of 3.4 nm,
• Watson and Crick - first produce a structure model of DNA that could account for all the experimental evidence.

Question 5

Explain how complementary base pairing maintains a constant width in a DNA molecule.

Answer 5

A pairs with T, A has 2 rings but T has 1. G pairs with C, G has 2 rings but C has 1. Because of the relative sizes of the bases that pair together, the double helix keeps a constant width.

Question 6

Explain the difference between the terms gene and genome.

Answer 6

Gene - defined as a functional sub-unit of DNA that directs the production of one or more polypeptides (protein molecules).

For example: Genes are not spaced regularly along , chromosomes.

Genome - of an organism is the sum of all the DNA that is carried in each cell of the organism. This DNA includes genes as well as regions of non-coding DNA, which may play various roles in gene expression.

For example: genome is about 3 billions base pairs, and it includes an estimated 20000 to 25000 genes.

Question 7

What is meant by the term “semi-conservative replication”?

Answer 7

This means that every double helix in the new generation of an organism consists of one complete “old” strand and one complete “new” strand wrapped around each other.

Question 8

Why does replication take place in a slightly different way on each DNA strand?

Answer 8

Replication occurs simultaneously at multiple places along a DNA strand. Because human DNA is so very long (with up to 80 million base pairs in a chromosome) it unzips at multiple places along its length so that the replication process is going on simultaneously at hundreds of places along the length of the chain.

Question 9

Explain how the leading and lagging strands of a DNA molecule are replicated.

Answer 9

During DNA replication, one new strand (the leading strand) is made as a continuous piece. The other (the lagging strand) is made in small pieces. DNA replication requires other enzymes in addition to DNA polymerase, including DNA primase, DNA helicase, DNA ligase, and topoisomerase.

Question 10

Describe the components of the replication machine.

Answer 10

Replication machineries include primosotors are replication enzymes; DNA polymerase, DNA helicases, DNA clamps and DNA topoisomerases, and replication proteins; e.g. single-stranded DNA binding proteins (SSB). In the replication machineries these components coordinate.

Question 11

In what way is the structure of a protein related to the structure of DNA?

Answer 11

It called amino acids - determines the chemical properties of each protein that are produced by a cell determine the structure, function, and development of the cell.

The genetic code - determines how the amino acids are strung together and how the protein are made.

Question 12

What are the two basic steps involved in gene expression?

Answer 12

DNA is copied into an RNA molecule in process called transcription

mRNA molecule moves into the cytoplasm of the cell, where the mRNA nucleotide sequence directs the synthesis of a polypeptide ( a chain of amino acids) with the aid of another RNA molecule, transfer RNA (tRNA) - translation

Question 13

How many bases make up each codon?

Answer 13

Codons are made up of any triplet combination of the four nitrogenous bases

adenine (A), guanine (G), cytosine (C), or uracil (U).

Question 14

Describe each characteristic of genetic code

a) redundant
b) continuous
c) universal

Answer 14

a) redundant - more than one codon can code for the same amino acid. Only three codons do not code for any amino acid. These codons serve as “stop” signals to end protein synthesis.
b) continuous - the genetic code reads as a series of three letter codons without speeches, punctuation, or overlap. Knowing exactly where to start and stop translation is therefore essential. A shift ozone or two nucleotides in either direction can alter the Condon groupings and results in an incorrect amino acid sequence.
c) universal - Almost all living organism build Peoria with the genetic code. The important implications for gene technology, since a gene that is taken from one kind of organism and inserted into another kind of organism will produce the same protein.

Question 15

Describe the role of RNA polymerase complex in transcription.

Answer 15

RNA polymerase is the main transcription enzyme. Transcription begins when RNA polymerase binds to a promoter sequence near the beginning of a gene (directly or through helper proteins). RNA polymerase uses one of the DNA strands (the template strand) as a template to make a new, complementary RNA molecule.

Question 16

What is the role of tRNA in translation?

Answer 16

Transfer RNAs (tRNAs) are adaptor molecules that translate genetic information into protein sequence by delivering amino acids to the protein synthesis machinery during translation.

Question 17

What feature of the genetic code helps to protect a cell from the effects of nucleotide substitution?

Question 18

What is a frameshift mutation?

Answer 18

• Cause the entire reading frame of the gene to be altered, a shift in the reading frame usually results in a nonsense mutation.
• Frameshift mutation in a gene refers to the insertion or deletion of nucleotide bases in numbers that are not multiples of three. This is important because a cell reads a gene’s code in groups of three bases when making a protein.

Question 19

Why mutation caused by an insertion or a deletion more likely to have serious consequences for a cell than one caused by a substitution?

Answer 19

Because an insertion or deletion results in a frame-shift that changes the reading of subsequent codons and, therefore, alters the entire amino acid sequence that follows the mutation, insertions and deletions are usually more harmful than a substitution in which only a single amino acid is altered.

Question 20

Distinguish between the two term in each pair in terms.

a) induced mutation and spontaneous mutation
b) chemical mutagen and physical mutagen

Answer 20

• Spontaneous mutations can occur because of replication errors or as a consequence of lesions introduced into DNA during normal cell growth.
• Induced mutations arise after treatment of the organism with an exogenous mutagen being physical or chemical agent increasing the frequency of mutations.
• Most chemical mutagens are alkylating agents and azides.
• Physical mutagens include electromagnetic radiation, such as gamma rays, X rays, and UV light, and particle radiation, such as fast and thermal neutrons, beta and alpha particles.

Question 21

Why is your mitochondria DNA identical to the mitochondrial DNA of your mother, rather than father?

Answer 21

The cytoplasm in a zygote is donated by the ovum. The sperm cell contributes essentially no cytoplasm, and therefore no cytoplasmic organelles, to its offspring.

While the DNA in the nuclei of your cells is made up of an equal combination of DNA from your mother and your father, your mtDNA is genetically identical to the mtDNA of your mother. Her mtDNA in turn, is identical to the mtDNA of her mother.

Question 22

Give two examples of ways that the study of DNA sequences can help scientists learn about genetic relationships, genetics variation, or evolutions.

Answer 22

• They helped understand of ancient ecosystems and track the evolution of a species through time.
• The study of biological diversity and evolution is the analysis of non-coding stretches tend to have a higher mutation rate than the DNA within gene.

Question 23

Explain why these characteristics of restriction endonuclease make these enzymes useful to genetic engineers.

a) specificity
b) staggered cuts

Answer 23

Specificity - Cuts made by an endonuclease are specific and predictable. The enzyme will cut a particular strand of DNA the same way each time, producing an identical set of small DNA fragments These small fragments are called restriction fragments

Staggered - Most restriction edonucleases produce a staggered cut that leaves a dew unpaired nucleotides on a single strand at each end of the restriction fragment. These short strands, often referred to as sticky ends, can then form base Paris with other short strands that have a complementary sequence.

Question 24

What is a DNA microarray, and for what purpose is it used?

Answer 24

• A chip (glass microscope slider or a polymer membrane) that contains a grid of thousands of microscopic cell
• DNA microarray allows scientists to analyze the activity of thousands of gene at one.

Question 25

What kind of information can a DNA microarray analysis provide?

Answer 25

DNA microarrays help in gene discovery, their expression profiling, their regulation, genetic disease screening, SNP discrimination, microbial detection and typing, and observe variation between transcript levels of genes under different conditions.

Question 26

How would medical researchers benefits from studying the human genome as a whole, rather than studying individual genes? Give an example.

Answer 26

The potential for developing drugs that are tailored not only to the expression of individual genes associated with particular disorders, but also to the unique genome of a patient.

Studying the differences in gene expression among the individuals can help medical researchers understand why certain drugs work better in some people than in others, and why certain people experience side effects from medications.

Question 27

How can transgenetic organism help to achieve social, economic, or environmental goals? Give on example of a transgenic plant, and transgenic animal designed for one of these goals?

Answer 27

• From the environment - farmers increase their crop yields and save money on herbicide application
• An example - Canola - which resistant to the herbicide Roundup.

Question 28

Give two examples of social, legal, or moral issues that are associated with the development of transgenic organisms.

Answer 28

An example is Human Insulin, a transgenic bacteria was approved for medical use in US, first example of a genetically engineered pharmenutical product.

An example is cloned and transgenic animals - organisms that are genetically identical are said to be clones of one another.

Question 29

What kind of genetic information can be obtained from each of the following procedures?

a) ultrasound
b) amniocentesis
c) DNA probe

Answer 29

a) Ultrasound - sound waves beyond the limit of human hearing are sent through the amniotic and it will bounce off the developing fetus and are to create a cross-sectional image of the fetus. The image can show physical abnormalities such as missing limb, malformed heart, and or cleft palate.
b) Amniocentesis - a needle is to used to withdraw a small sample of amniotic fluid from the uterus. The extracted fluid is place in a special nutrient rich-medium and the cells are allowed to multiply.
c) DNA probe - consists of a molecule of DNA with a nucleic acid sequence that is complementary to the marker sequence “marked” wot a radioactive or fluorescent chemical tag.