Molecular Biology Quiz: DNA and RNA Concepts

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What replaces T in the mRNA sequence when compared to the DNA sequence?

U (uracil) replaces T (thymine) in the mRNA sequence.

What is the role of the antisense strand in mRNA production?

The antisense strand serves as the template for mRNA production and is complementary to the RNA transcript.

Define tandem repeats and give examples of their types.

Tandem repeats are stretches of repeated DNA sequences; examples include satellites, minisatellites, and microsatellites.

How do tandem repeats arise during DNA replication?

Tandem repeats arise through replication slippage, which can involve either backward or forward slippage. Signup and view all the answers

What are transposons and why are they referred to as 'jumping genes'?

Transposons are mobile genetic elements that can move within the genome, hence they are called 'jumping genes'. Signup and view all the answers

What is the role of the centromere in chromosome structure?

The centromere holds sister chromatids together and is essential for spindle attachment during segregation. Signup and view all the answers

How do telomeres contribute to chromosome stability?

Telomeres maintain the structural integrity of chromosomes and prevent loss during DNA replication. Signup and view all the answers

What distinguishes purines from pyrimidines in the structure of nucleotides?

Purines include adenine (A) and guanine (G), while pyrimidines comprise cytosine (C) and thymine (T). Signup and view all the answers

Describe the function of the sense strand in gene structure.

The sense strand is the coding strand, and its sequence directly determines the corresponding protein sequence during transcription. Signup and view all the answers

In addition to protein-coding genes, what types of functional RNAs are encoded in the human genome?

The human genome encodes for rRNAs, tRNAs, small nuclear RNAs, small nucleolar RNAs, and microRNAs. Signup and view all the answers

What percentage of the human genome is represented by the exome?

2% Signup and view all the answers

Describe the difference in structure between mitochondrial DNA and nuclear DNA.

Mitochondrial DNA is circular while nuclear DNA is linear. Signup and view all the answers

What are the primary roles of the 13 genes encoded by mitochondrial DNA?

They code for enzymes involved in oxidative phosphorylation. Signup and view all the answers

What are histones and their role in chromosome structure?

Histones are basic proteins around which DNA is wrapped to form nucleosomes. Signup and view all the answers

Differentiate between heterochromatin and euchromatin.

Euchromatin is transcriptionally active and less condensed, while heterochromatin is condensed and usually inactive. Signup and view all the answers

What is the mutation rate of mitochondrial DNA compared to nuclear DNA?

Mitochondrial DNA has a mutation rate 10 to 100 times higher than nuclear DNA. Signup and view all the answers

How is mitochondrial DNA inherited?

Mitochondrial DNA is inherited maternally. Signup and view all the answers

What is the total length of the mitochondrial genome in base pairs?

16,569 base pairs. Signup and view all the answers

Study Notes

Human Genome Organisation

Human DNA, stretched out, measures approximately 6 feet (1.8 meters)

The Human Genome

The nuclear genome is 3.2 Gb
The mitochondrial genome is 16.5 Kb
25% of the genome is genes and related DNA
75% of the genome is extragenic DNA
10% of the genome is coding and regulatory DNA
90% of the genome is non-coding DNA
60% of the genome is unique low copy number DNA
40% of the genome is repetitive DNA
The exome comprises 2% of the genome
Functional RNAs present in the genome include rRNAs, tRNAs, small nuclear RNAs, small nucleolar RNAs and microRNAs

The Mitochondrial Genome

A single double stranded (ds) circular chromosome
Contains 2-10 copies per mitochondrion
Contains 16,569 bp
Contains 37 genes; 13 code for oxidative phosphorylation enzymes; 2 code for mt rRNAs and 22 code for mt tRNAs

mtDNA vs Nuclear DNA

mtDNA is circular, nuclear DNA is linear
mtDNA has no introns, nuclear DNA has introns
mtDNA has small intergenic spaces (1-2bp), nuclear DNA has large intergenic spaces (Kb)
mtDNA codon usage differs from nuclear DNA’s
mtDNA is maternally inherited, nuclear DNA is inherited from both parents
mtDNA replicates rapidly, nuclear DNA replicates more slowly
mtDNA has no proof-reading or DNA repair, nuclear DNA does
mtDNA mutation rate is high (10-100x) compared to nuclear DNA

Chromosomes: Structure

Chromosomes are composed of DNA, which is organized into nucleosomes
A chromosome during duplication includes DNA synthesis
A chromosome has two sister chromatids that are joined at the centromere
The chromatids separate at the centromere
A chromosome has telomeres which are located at the chromosomal tips

Chromosomes: Organisation

Chromosomes have loops of chromatin
Nucleosomes are 10nm in diameter
A 30nm chromatin fiber is made from folded nucleosomes.
DNA is organized into a double helix
The diameter of a double helix is 2nm

Histones

Histones are small (10-20 kDa)
Histones are highly conserved
Histones are very basic proteins
Histones are heavily acetylated/methylated
Eight (8) histones form a core around which DNA is wrapped
Histones are attached to linker DNA.
Histones do not dissociate from DNA during DNA replication.

Heterochromatin & Euchromatin

Euchromatin is the fraction of DNA that is transcriptionally active and adopts a relatively extended conformation.
Heterochromatin is a chromosomal region that remains condensed throughout the cell cycle and shows litle or no active gene expression
Heterochromatin is either constitutive (always inactive) e.g., the centromere, or facultative (can be condensed or dispersed) - e.g., the mammalian X-chromosome
Histone modifications, in chromatin, affect gene expression

The Centromere

The centromere is the chromosomal constriction where sister chromatids are joined
The centromere is essential for chromosome attachment to the spindle and segregation
The centromere contains highly repetitive specific DNA sequences

The Telomere

Telomeres are the tips of chromosomes
They are composed of repetitive DNA sequences
Essential for maintaining the integrity of chromosomes
Telomeres are linked to ageing
Telomerase is needed to prevent loss of telomeres during DNA replication

Nucleotides

There are two purines: Adenine (A) and Guanine (G)
There are two pyrimidines: Cytosine (C), and Thymine (T)
Uracil (U) replaces Thymine (T) in RNA

Different Sugars in DNA and RNA

DNA has 2-deoxyribose, RNA has ribose
The sugar differs by the presence or absence of a hydroxyl group

DNA – RNA – Protein Synthesis

Transcription generates RNA from DNA
RNA splicing removes introns from RNA
Translation synthesizes proteins from RNA

Genes in the human genome

The human genome contains approximately 21,306 protein-coding genes
In addition to protein-coding genes, the human genome codes for functional RNAs (e.g., rRNA, tRNA, snRNA, snoRNA, miRNA)

Gene Structure

Genes comprise a control region and protein coding regions
The control region contains binding sites for transcription factors
Protein coding regions have universal and basal transcription factors , a promoter, and a transcription initiation site, as well as stop signals.

Sense and antisense DNA strands

The sense strand is the coding strand; its sequence determines the protein sequence
The antisense strand serves as the template for mRNA production
The sequence is the same as the mRNA except for T being replaced by U.
Strands are always read 5'→3'

Non-coding RNA

Non-coding RNA is RNA that does not encode proteins
Positional classification of ncRNA includes intergenic, intronic, and exonic ncRNA

Repetitive DNA

Repetitive DNA sequences exist as tandem repeats or short simple repeats (SSRs).
Examples of repetitive DNA include satellites, minisatellites, and microsatellites.

How do Tandem Repeats arise?

Tandem repeats can arise from replication slippage (polymerase stuttering).

Mobile Genetic Elements

Mobile genetic elements include transposons (jumping genes), which can move around the genome, often flanked by short, inverted repeats sequences.
Retrotransposons are a type of transposon which move via an RNA intermediate.
Transposable elements (TEs) can give rise to repetitive genomic DNA, including pseudogenes.

Pseudogenes

Pseudogenes are non-functional copies of protein-coding genes arising through reverse transcription of mRNAs.
Pseudogenes may have arisen through gene duplication.
Pseudogenes can have serious implications for genetic diagnostics.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on key concepts of DNA and RNA, including the roles of various strands and sequences in mRNA production. This quiz also covers structural differences between mitochondrial and nuclear DNA, as well as the functions of histones, centromeres, and telomeres. Explore the fascinating world of genetics with questions on transposons, repeat sequences, and functional RNAs.