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core idea for one gene-one enzyme is

that a gene typically specifies a protein in a one-to-one relationship

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Genetics - Details



63 questions
His is a non-fatal disorder where a person’s urine turns black because they cannot break down a molecule called alkapton (which, in normal people without the disorder, gets broken down into other, colorless molecules)
Sir Archibald Garrod,
A British medical doctor, was the first to suggest that genes were connected to enzymes. the first to have linked genes with the enzymes that carry out metabolic reactions.
“inborn error of metabolism,”
Are rare genetic (inherited) disorders in which the body cannot properly turn food into energy. The disorders are usually caused by defects in specific proteins (enzymes) that help break down (metabolize) parts of food.
"one gene-one enzyme” hypothesis. This hypothesis has undergone some important updates since Beadle and Tatum
1. Some genes encode proteins that are not enzymes. Enzymes are just one category of protein. There are many non-enzyme proteins in cells, and these proteins are also encoded by genes. 2. Some genes encode a subunit of a protein, not a whole protein. In general, a gene encodes one polypeptide, meaning one chain of amino acids. Some proteins consist of several polypeptides from different genes 3. Some genes don't encode polypeptides. Some genes actually encode functional RNA molecules rather than polypeptides!
Core idea for one gene-one enzyme is
That a gene typically specifies a protein in a one-to-one relationship
Is the study of inherited traits, including those partially influenced by environment
Is the study of all the genes in an organism to understand their molecular organization, function, interaction, and evolutionary history
Are the basic elements of heredity
Gregor Mendel
The existence of genes was first suggested by the work of Gregor Mendel in 1866
Classical genetics
Is the approach to the study of genetics through analysis of the offspring of matings
Friedrich Miescher
Discovered DNA in leukocytes in 1869
Molecular genetics
Is the analysis of differences between species through the study of DNA itself
The importance of cell nuclei was recognized when it was observed that they undergo fusion in fertilization of male and female gametes
The importance of chromosomes was deduced from their „splitting“ behavior during cell division and their constant number characteristic for every species
Early 20th century
Chromosomes contain DNA and protein The kinds of protein present differ by cell type DNA was thought to lack the chemical diversity needed for the genetic material The diversity of proteins was the reason for the belief that they are the genetic material This was proven wrong in a series of experiments
Frederick Griffith (1928)
He demonstrated that the genetic material can be transferred from living R cells into killed S cells made them able again to cause the illness in mouse.
Avery, MacLeod and McCarty (1944)
Showed that the substance causing the transformation of R cells into S cells was DNA, so that DNA is the genetic material.
Hershey and Chase, the „blender“ experiment (1952)
Experiment demonstrating that DNA is the active material in bacterial transformation.
James Watson and Francis Crick (1953)
Right-handed (B-form) DNA structure Double-stranded molecule Duplex polarity and base complementarity (Watson-Crick base-pairing)
Three conclusions on the properties of DNA:
DNA is capable of replication through complementary base pairing The order of bases in a DNA molecule is the source of variation Mutations arise from mistakes in copying DNA
Are made according to instructions given in DNA sequence
Variety functions of Proteins
Trafficking Structure Signalling and receptor molecules Metabolic processes Enzymatic role
Were first defined as proteins by Emil Fischer in 1900 and led to define inborn errors of metabolism
Inborn errors of metabolism
Were studied in terms of hereditary diseases
Archibald Garrod (1908)
Alkaptonuria – relatively benign excretion of homogentisic acid (previously known as alkapton) that turns urine black due to oxidation reaction
The S type of S. pneumoniae
Synthesizes a gelatinous capsule composed of complex carbohydrate (polysaccharide) appear large glistening and smooth capable of causing illness
The enveloping capsule makes each colony large
And gives it a glistening or smooth ( S) appearance
The R strains of S. pneumoniae are
Unable to synthesize the capsular polysaccharide and that's why they look small and rough not causing illness
The R strain of the bacterium does not cause pneumonia, because
Without the capsule the bacteria are inactivated by the immune system of the host.
DNA contains
Phosphorus but no sulfur
Most proteins contain
Sulfur but no phosphorus
In the Watson-Crick structure
DNA consists of two long chains of subunits, each twisted around the other to form a double-stranded helix.
The double helix is right-handed, meaning
DNA is moving in clockwise direction
What do each nucleotides contains
Any one of four chemical constituents called bases
Bases are attached to
To a phosphorylated molecule of the 5-carbon sugar deoxyribose
4 bases in DNA are
Adenine (A) Guanine (G) Thymine (T) Cytosine (C)
So what is this complementary pairing
Each base along one strand of the DNA is matched with a base in the opposite position on the other strand.
Strands are running in
Opposite directions 5'-3' and other one is 3'-5'
DNA is running in which directions
Opposite directions from 5'-3' or from 3'-5'
What is DNA replication
The copying process in which a single DNA molecule gives rise to two identical molecules
Why proteins are important
What is created from the complex and diverse DNA codes is protein, a class of macromolecules that carries out most of the biochemical activities in the cell.
Give some examples for functions of proteins
These include structural proteins that give the cell rigidity and mobility proteins that form pores in the cell membrane to control the traffic of small molecules into and out of the cell receptor proteins that regulate cellular activities in response to molecular signals from the growth medium or from other cells. Proteins are also responsible for most of the metabolic activities of cells. They are essential for the synthesis and breakdown of organic molecules and for generating the chemical energy needed for cellular activities.
Inborn errors of metabolism
Term is commonly used today, to identify those hereditary diseases which arise as a consequence of deregulation of enzymatic activity.
The disease itself is relatively mild, but it has one striking symptom
The urine of the patient turns black because of the oxidation of homogentisic acid. This is why alkaptonuria is also called black urine disease
As to the biochemistry, he deduced that the problem in alkaptonuria
Was the patients' inability to break down the phenyl ring of six carbons that is present in homogentisic acid.
Where does this ring come from?
Garrod proposed that homogentisic acid originates as a breakdown product of two amino acids, phenylalanine and tyrosine, which also contain a phenyl ring.
Amino acid
Is one of the "building blocks" from which proteins are made
Metabolic or biological pathway
Any such sequence of biochemical reactions
Metabolic pathway for the breakdown of phenylalanine and tyrosine. Each step in the pathway, represented by an arrow, requires a specific enzyme to catalyze the reaction. The key step in the breakdown of homogentisic acid is the breaking open of the phenyl ring.
What did inborn errors of metabolism affect
Inborn errors of metabolism that affect the breakdown of phenylalanine and tyrosine. An inherited disease results when any of the enzymes is missing or defective. Alkaptonuria results from a mutant homogentisic acid 1,2d1oxygenase; phenylketonu ria results from a m utant phenyla lanine hydroxylase.
The gene PAH
On the long arm of chromosome 12 encodes phenylalanine hydroxylase (PAH)
The gene TAT
On the long arm of chromosome 16 encodes tyrosine aminotransferase (TAT
The gene HPD
On the long arm of chromosome 12 encodes 4-hydroxyphenylpyruvic acid dioxygenase (HPD).
The gene HGD
On the long arm of chromosome 3 encodes homogentisic acid 1,2 dioxygenase (HGD).
What did George W. Beadle and Edward L. Tatum identified
In these experiments, they identified new mutations that each caused a block in the metabolic pathway for the synthesis of some needed nutrient, and showed that each of these blocks corresponded to a defective enzyme needed for one step in the pathway
Archibald Garrod
Garrod worked with patients who had metabolic diseases and saw that these diseases often ran in families.
Minimal medium
Because it contains only the nutrients that are essential for growth of the organism.
Explain the experiment beadle and tatum
Beadle and Tatum obtained mutants of the filamentous fungus Neurospora crassa by exposing asexual spores to x-rays or ultraviolet light. The treated spores were used to start the sexual cycle in fruiting bodies. After any pair of cells and their nuclei undergo fusion, meiosis takes place almost immediately and results in eight sexual spores (ascospores) included in a single ascus. These are removed individually and cultured in complete medium. Ascospores that carry new nutritional mutants are identified later by their inability to grow in minimal medium.
A)test for nutritional mutants b)test for required nutrient c)test for specific amino acid d)test for arginine precursor
(A) Mutant spores can grow in complete medium but not in minimal medium. (B) Each new mutant is tested for growth in minimal medium supplemented with a mixture of nutrients. (C) Mutants that can grow on minimal medium supplemented with amino acid are tested with each amino acid individually. (D) Mutants unable to grow in the absence of arginine are tested with likely precursors of arginine.
Complementation test
Mutations that have defects in the same gene are identified by means of a complementation test, in which two mutations are brought together into the same cell.
If it grows in minimal medium, the mutant genes are said to undergo
If the heterokaryon fails to grow in minimal medium, the result indicates
Heterokaryon formation
Molecular interpretation of a complementation test using heterokaryons to determine whether two mutant strains have mutations in different genes (A) or mutations in the same gene (B). In (A) each nucleus contributes a non mutant form of one or the other polypeptide chain, and so the heterokaryon is a ble to grow in minimal medium. In (B) both nuclei contribute a mutant form of the same polypeptide chain; hence, no non mutant form of that polypeptide can be synthesized and the heterokaryon is unable to grow in minimal medium.
A method for interpreting the results of complementation tests.
Arrange the mutations in a circle. (B) Connect by a straight line any pair of mutations that fail to complement-that is, that yield a mutant heterokaryon. Any pair of mutations connected by a straight line are mutations in the same gene, and are more than likely mutations at different nucleotide sites in the gene. This example shows two complementation groups, each of which represents a single gene needed for arginine biosynthesis.
Polypeptide chain
A typical protein is made up of one or more polypeptide chains
The "central dogma" of molecular genetics:
DNA codes for RNA, and RNA codes for protein. The DNA ---> RNA step is transcription, and the RNA ---> protein step is translation
Are there differences and if there what are they
There is a difference in the sugar (RNA contains the sugar ribose instead of deoxyribose), RNA is usually single-stranded (not a duplex), and RNA contains the base uracil (U) instead of thymine (T), which is present in DNA.
Three types of RNA take part in the synthesis of proteins:
Messenger RNA (mRNA) ribosomal RNA (rRNA) transfer RNA (tRNA)
Carries the genetic information from DNA and is used as a template for polypeptide synthesis
Major constituents of the cellular particles called ribosomes on which polypeptide synthesis takes place
Carries a particular amino acid as well as three base recognition region that base-pairs with a group of three adjacent bases in the mrna
The process of making an RNA strand from a DNA template is
The synthesis of a polypeptide under the direction of an mRNA molecule is known a
Translation process
Translation is mediated by transfer RNA (tR NA) molecules, each of which can base-pair with a group of three adjacent bases in the mRNA. Each tRNA also carries an amino acid. As each tRNA, in turn, is brought to the ribosome, the growing polypeptide chain is elongated
Start codon
Methionine AUG
Stop codons
Refers to any heritable change in a gene (or, more generally, in the genetic material) or to the process by which such a change takes place.
One type of mutation
Results in a change in the sequence of bases in DNA. The change may be simple, such as the substitution of one pair of bases in a duplex molecule for a different pair of bases.
Explain The M lV mutant in the PAH gene.
The methionine codon needed for initiation mutates into a codon for valine. Translation cannot be initiated, and no PAH polypeptide is produced.
Explain The R408W mutant in the PAH gene.
Codon 408 for arginine (R) is mutated into a codon for tryptophan (W). The result is that position 408 in the mutant PAH polypeptide is occupied by tryptophan rather than by argin ine. The m utant protein has only a low level of PAH enzyme activity.
All creatures on Earth share many features of the genetic apparatus
, including genetic information encoded in the sequence of bases in DNA, transcription into RNA, and translation into protein on ribosomes with the use of transfer RNAs.
One gene can affect more than one trait
Pleiotropy ex: PKU and fair skin/blonde hair
All creatures also share certain characteristics in their biochemistry,
Including many enzymes and other proteins that are similar in amino acid sequence, three-dimensional structure, and function.