Genetics Basics Quiz

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Questions and Answers

What is a gene primarily defined as?

A unit of genetic information transmitted to descendants (correct)

An alternative form of a chromosome

The observable properties of an organism

A structure carrying hereditary information

Which of the following best describes a homozygote?

Individual with a unique genetic makeup

Individual with identical alleles at one or more loci (correct)

Individual with different alleles at one or more loci

Individual containing multiple chromosomes

In Griffith's experiment, what type of bacteria was used as a control in the study?

Non-virulent RII strain (correct)

Live virulent S strain

Virulent SIII strain

Heat-killed SIII strain

What conclusion can be drawn from Griffith's findings?

Heat-killed SIII bacteria can convert RII bacteria into SIII Signup and view all the answers

Which characteristic distinguishes virulent strains of bacteria from non-virulent ones in Griffith's experiment?

Presence of a polysaccharide capsule Signup and view all the answers

What does the phenotype of an organism refer to?

Observable properties that are genetically controlled Signup and view all the answers

What type of colonies do encapsulated bacteria produce on agar plates?

Smooth colonies Signup and view all the answers

What is the primary role of chromosomes in cells?

They store genetic information Signup and view all the answers

What is the main component that determines hereditary characteristics in the TMV virus?

RNA Signup and view all the answers

Which of the following nucleotides is found only in RNA?

Uracil Signup and view all the answers

What type of sugar is found in ribonucleic acid (RNA)?

Ribose Signup and view all the answers

Which statement accurately describes the structure of nucleotides?

They are formed by adding a phosphate group to a nucleoside. Signup and view all the answers

Which feature distinguishes purines from pyrimidines?

Purines contain a double carbon ring structure. Signup and view all the answers

How are two mononucleotides linked together?

Via a phosphate group attached to the sugar. Signup and view all the answers

What forms when a nucleoside has one or more phosphate groups added to it?

Nucleotide Signup and view all the answers

Which of the following is a key role of triphosphate nucleotides in the cell?

They act as precursors for nucleic acid synthesis. Signup and view all the answers

What is the main function of DNA in organisms?

It serves as the carrier of genetic information. Signup and view all the answers

Which scientist is known for establishing the pairing rules between adenine and thymine as well as guanine and cytosine?

Erwin Chargaff Signup and view all the answers

What does the Chargaff ratio A + G = T + C indicate?

The total amount of purines equals the total amount of pyrimidines. Signup and view all the answers

What was Rosalind Franklin's contribution to the understanding of DNA's structure?

She suggested that DNA might be a helical structure based on X-ray diffraction. Signup and view all the answers

What is the significance of the Chargaff coefficient A + T / C + G?

It varies and provides information about the base richness of DNA. Signup and view all the answers

Which of the following pairs are equal according to Chargaff's findings?

The amount of adenine and thymine. Signup and view all the answers

What did Chargaff find regarding the ratios of bases in different organisms?

The ratios vary considerably between species. Signup and view all the answers

What type of bond forms the backbone of a DNA molecule?

Phosphodiester bonds Signup and view all the answers

What property causes nucleic acids to migrate towards the positive pole during electrophoresis?

Negatively charged phosphate groups Signup and view all the answers

At which wavelength do nucleic acids absorb UV light primarily?

254-260 nm Signup and view all the answers

What happens to DNA strands during denaturation?

The strands separate as hydrogen bonds break Signup and view all the answers

Why is G≡C pairing more stable than A=T pairing?

It has an extra hydrogen bond Signup and view all the answers

Which of the following is NOT required for in vitro DNA synthesis as identified by Kornberg's experiments?

RNA polymerase Signup and view all the answers

In which direction does DNA synthesis occur?

5' to 3' Signup and view all the answers

What type of model did Watson and Crick propose for DNA replication?

Semi-conservative model Signup and view all the answers

Which process occurs during the renaturation of DNA?

Strands reassociate upon cooling Signup and view all the answers

What role does telomerase play in chromosome replication?

It recognizes and extends repetitive sequences at telomeres. Signup and view all the answers

What is the primary structural unit of eukaryotic chromatin?

Nucleosome Signup and view all the answers

What happens to the end of a chromosome during DNA synthesis if a 3'-OH group is not provided?

The chromosome may shorten with each replication cycle. Signup and view all the answers

How is bacterial DNA typically organized?

As a single circular double-stranded DNA molecule. Signup and view all the answers

Which of the following statements is true regarding mitochondrial DNA?

It is circular and organized into nucleoids. Signup and view all the answers

What is a characteristic feature of plasmids in bacteria?

They are small, circular extrachromosomal DNA molecules. Signup and view all the answers

What type of amino acids are histones rich in?

Basic amino acids Signup and view all the answers

What structural component is present in both bacterial chromosomes and plasmids?

Circular DNA organization Signup and view all the answers

Study Notes

Genetic Material

Genetics is the study of heredity and the expression of inherited traits.
Genes are units of genetic information passed down to descendants, specifying synthesis of RNA or polypeptide chains.
Genomes encompass all genetic information of a species, represented by the DNA of a haploid chromosome set.
Chromosomes are structures composed of DNA and associated proteins, carrying hereditary information.
Alleles are alternate forms of a gene. Diploid cells possess two alleles per gene, located at the same locus on homologous chromosomes.
Genotype refers to the specific allelic composition of an organism, often focusing on a single gene or a limited set.
Phenotype describes the observable traits of an organism that are genetically determined.
Homozygous individuals have identical alleles at one or more loci, producing identical gametes and constituting pure lines.
Heterozygous individuals possess different alleles at one or more loci, generating diverse gametes and lacking pure lines.

Griffith's Experiment (1927)

Griffith studied different strains of Diplococcus pneumoniae (now Streptococcus pneumoniae).
Some strains were virulent (pathogenic), causing pneumonia, while others were non-virulent.
Virulent strains possess a polysaccharide capsule, preventing phagocytosis by mouse phagocytes.
Encapsulated bacteria form smooth (S) colonies, while non-encapsulated bacteria form rough (R) colonies.
Griffith used serotypes II and III.
Mice injected with live, non-virulent RII bacteria did not develop pneumonia, suggesting RII couldn't transform into SIII.
Heat-killed SIII bacteria could convert live RII bacteria into virulent SIII bacteria, demonstrating a transfer of genetic information.

Structure of Nucleic Acids

Nucleic acids are polymers of nucleotides (polynucleotide chains).
Nucleotides consist of a nitrogenous base, a pentose sugar (5-carbon sugar), and a phosphate group.
Nucleic acids contain two purines: adenine (A) and guanine (G).
Nucleic acids contain three pyrimidines: cytosine (C), uracil (U), and thymine (T).
Ribonucleic acid (RNA) contains ribose as its sugar.
Deoxyribonucleic acid (DNA) contains deoxyribose as its sugar.
A purine or pyrimidine base linked to ribose or deoxyribose forms a nucleoside.
Adding a phosphate group to a nucleoside creates a nucleotide.
Nucleotides can be further modified by the addition of one or two phosphate groups, forming diphosphate nucleosides (NDP) and triphosphate nucleosides (NTP).
NTPs, specifically the triphosphate form, act as precursors for nucleic acid synthesis in cells.
Two nucleotides are linked via a phosphodiester bond between their sugars, forming a dinucleotide.
A polynucleotide chain consists of multiple nucleotides linked by phosphodiester bonds.

Structure of Deoxyribonucleic Acid (DNA)

DNA carries genetic information in all organisms except certain viruses.
Erwin Chargaff, Maurice Wilkins, Rosalind Franklin, Linus Pauling, Francis Crick, and James Watson contributed significantly to understanding DNA structure and function.

Base Composition Study by Erwin Chargaff (1950)

Chargaff used chromatography to separate nitrogenous bases from DNA samples.
Adenine (A) quantity is proportional to thymine (T) quantity in various species.
Guanine (G) quantity is proportional to cytosine (C) quantity.
Purine sum (A+G) equals pyrimidine sum (C+T).
Percentage of C + G doesn't necessarily equal percentage of A + T, varying between species.

X-Ray Diffraction Analysis

Rosalind Franklin conducted X-ray diffraction studies on DNA, suggesting a helical structure.

Physicochemical Properties of Nucleic Acids

Nucleic acids are negatively charged due to phosphate groups, migrating towards the positive pole in an electric field.
Nucleic acids absorb UV light between 254-260 nm wavelengths due to interactions with purine and pyrimidine cycles, with maximum absorption at 260 nm.
DNA can undergo denaturation where hydrogen bonds between strands break, separating the strands, resulting in increased UV absorption.
Renaturation involves the reassociation of complementary strands when cooled.
G≡C pairing is more stable than A=T pairing due to an extra hydrogen bond.
Nucleases and chemical reagents can degrade nucleic acids.

DNA Replication in Prokaryotes and Eukaryotes

Replication is the synthesis of DNA, copying a parent DNA molecule into two identical daughter molecules.
Arthur Kornberg and collaborators identified in vitro requirements for DNA synthesis:
- Four deoxyribonucleoside triphosphates (dNTPs: dATP, dCTP, dGTP, dTTP)
- A double-stranded DNA template
- DNA polymerase I (isolated from E. coli)
- Mg++ ions
DNA synthesis proceeds in the 5' to 3' direction.
Watson and Crick proposed that unwound DNA strands serve as templates for complementary strand synthesis.

Replication Models

Three proposed replication models exist:
- Conservative: Parent DNA stays intact, while a new double helix is formed.
- Semi-conservative: Each daughter DNA molecule contains one parental strand and one newly synthesized strand.
- Dispersive: Both daughter helices contain a mixture of parental and newly synthesized DNA segments.

Telomerase

Enzyme that replicates chromosome ends by recognizing repetitive sequences and extending them in the 5' to 3' direction.
These repeats form a "hairpin loop," creating a 3'-OH group that serves as a substrate for DNA polymerase I, preventing DNA loss during replication.

Chromosome Organisation

Viral Chromosomes consist of single- or double-stranded DNA or RNA, existing in linear or circular forms and associated with proteins.
Bacterial Chromosomes are double-stranded, typically circular, organized into supercoils, and associated with proteins to form the nucleoid, the region containing DNA within the cytoplasm.
Plasmids: Small, circular, extrachromosomal double-stranded DNA molecules found in bacteria.
Eukaryotic Nuclear DNA is carried on chromosomes, each composed of a single DNA molecule wrapped around histone proteins.
Chromatin: Complex of DNA, histones, and non-histone proteins found within the nucleus of eukaryotic cells.
Nucleosome: Bead-like structure of eukaryotic chromatin, consisting of DNA wrapped around a histone core, representing the fundamental unit of chromatin.
Histones: Proteins rich in basic amino acids (arginine and lysine) that facilitate DNA wrapping into nucleosomes.

Mitochondrial DNA

Double-stranded and circular, organized into nucleoids, and not associated with histones.

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Description

Explore the fundamental concepts of genetics in this quiz, including genes, alleles, genomes, and the differences between genotype and phenotype. Test your understanding of heredity, genetic traits, and the structures involved in inheritance. Ideal for students studying genetics or anyone interested in the science of heredity.