Biochemistry I - DNA Functions and Structure
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Questions and Answers

What is the distance spanned by one complete turn of the B form of DNA?

  • 34 Å (correct)
  • 10 Å
  • 3.4 Å
  • 20 Å

Which enzyme is primarily responsible for DNA replication?

  • DNA polymerase (correct)
  • DNA helicase
  • RNA polymerase
  • DNA ligase

How many base pairs are included in one complete turn of the B form of DNA?

  • 12 base pairs
  • 10 base pairs (correct)
  • 8 base pairs
  • 5 base pairs

In the structure of DNA, what do the short arrows represent?

<p>Polarity of the antiparallel strands (C)</p> Signup and view all the answers

What is the rise in angstroms per base pair in the B-DNA structure?

<p>3.4 Å (A)</p> Signup and view all the answers

What type of macromolecule is primarily responsible for biological inheritance?

<p>Nucleic acids (A)</p> Signup and view all the answers

What are the two types of grooves in the double helix of DNA called?

<p>Major and minor grooves (A)</p> Signup and view all the answers

Which component is NOT part of the structure of a nucleotide in DNA?

<p>Ribose sugar (C)</p> Signup and view all the answers

What is the primary function of synthetic oligonucleotide primers in the PCR process?

<p>To hybridize with complementary DNA sequences and define the synthesis region (B)</p> Signup and view all the answers

Which component of the PCR reaction is responsible for synthesizing new DNA strands?

<p>Heat-stable DNA polymerase (D)</p> Signup and view all the answers

What is the role of Mg(II) ions in a PCR reaction?

<p>To ensure optimal reaction conditions (B)</p> Signup and view all the answers

Which of the following statements correctly describes the composition of dNTPs in PCR?

<p>They include dCTP, dATP, dGTP, and dTTP in equal amounts (C)</p> Signup and view all the answers

In what order does transcription occur during RNA synthesis?

<p>Initiation, elongation, termination (A)</p> Signup and view all the answers

RNA transcripts are complementary to which strand of DNA during transcription?

<p>Only the template strand (C)</p> Signup and view all the answers

Which of the following statements is true regarding the RNA transcript's polarity?

<p>It is complementary to the coding strand and has a 5' to 3' polarity (D)</p> Signup and view all the answers

What distinguishes Real-Time PCR from other PCR types?

<p>It quantifies the DNA in real-time during the amplification process (D)</p> Signup and view all the answers

What is the main role of the 5' cap on mRNA?

<p>To stabilize mRNA and aid in recognition by the translating machinery (B)</p> Signup and view all the answers

Which characteristic of mRNA allows it to be recognized by translating machinery?

<p>Capping by 7-methylguanosine triphosphate (B)</p> Signup and view all the answers

What is the function of the poly(A) tail in mRNA?

<p>To stabilize mRNA by preventing the attack of 3'-exonucleases (A)</p> Signup and view all the answers

The relationship between an RNA transcript and its gene typically shows what kind of polarity?

<p>The RNA has 5' to 3' polarity while the template strand has 3' to 5' (A)</p> Signup and view all the answers

What is one proposed function of the poly(A) tail at the 3' end of mRNA?

<p>It may protect against 3'-exonucleolytic degradation (A)</p> Signup and view all the answers

Which statement about mRNA is true regarding its variability?

<p>mRNA molecules can vary greatly in size and stability (C)</p> Signup and view all the answers

Which feature is NOT typically associated with eukaryotic mRNAs?

<p>Direct translation without processing (B)</p> Signup and view all the answers

What happens to the 5' cap during mRNA translation?

<p>It facilitates the recognition and binding of ribosomes (A)</p> Signup and view all the answers

What must occur before mRNA can enter the cytoplasm in mammalian cells?

<p>It must be processed from a precursor molecule. (A)</p> Signup and view all the answers

What is the primary function of the cap structure at the 5′ terminal of mRNA?

<p>To aid in mRNA translation and stability. (C)</p> Signup and view all the answers

How do heterogeneous nuclear RNA (hnRNA) molecules differ from mRNA in terms of molecular weight?

<p>hnRNA typically has a molecular weight over 10 million, while mRNA is less than 2 million. (B)</p> Signup and view all the answers

What process is described by the translation of mRNA into a polypeptide chain?

<p>Decoding of mRNA into a specific sequence of amino acids. (B)</p> Signup and view all the answers

Which of the following is true regarding hnRNA modifications?

<p>They undergo processing to become mRNA. (B)</p> Signup and view all the answers

What characterizes the immediate products of gene transcription in mammalian nuclei?

<p>They are heterogeneous nuclear RNA molecules. (A)</p> Signup and view all the answers

Why are modifications such as a 7-methylguanosine added to mRNA after transcription?

<p>To protect mRNA from degradation. (A)</p> Signup and view all the answers

What roles do ribosomes play in cellular function?

<p>They translate mRNA into polypeptides. (D)</p> Signup and view all the answers

What is the correct sequence of phases in translation?

<p>Initiation, Elongation, Termination (B)</p> Signup and view all the answers

Which component is essential for linking the mRNA sequence to the amino acids during protein synthesis?

<p>Transfer RNA (tRNA) (C)</p> Signup and view all the answers

What happens during the elongation phase of translation?

<p>Amino acids are joined together to form a chain. (D)</p> Signup and view all the answers

What structural feature allows tRNA to form a cloverleaf shape?

<p>Intrastrand complementarity (B)</p> Signup and view all the answers

How many species of tRNA molecules are typically present in a cell?

<p>20 species (C)</p> Signup and view all the answers

What role does the acceptor arm of tRNA play?

<p>It attaches the appropriate amino acid. (A)</p> Signup and view all the answers

What occurs during the initiation phase of translation?

<p>The ribosome assembles around the target mRNA. (C)</p> Signup and view all the answers

What is a characteristic of tRNA in eukaryotic cells compared to prokaryotic cells?

<p>Less stable in eukaryotes than prokaryotes (D)</p> Signup and view all the answers

What is the status of mRNA stability in prokaryotes compared to eukaryotes?

<p>Unstable in prokaryotes but generally stable in eukaryotes (C)</p> Signup and view all the answers

Which statement accurately describes the composition of the 60S ribosomal subunit?

<p>Houses 5S, 5.8S, and 28S rRNA along with over 50 polypeptides (A)</p> Signup and view all the answers

Which rRNA is independently transcribed in the mammalian ribosome assembly?

<p>5S rRNA (C)</p> Signup and view all the answers

In which part of the cell do all ribosomal RNA molecules, except for the 5S rRNA, get processed?

<p>Nucleolus (A)</p> Signup and view all the answers

What is the molecular weight of a mammalian ribosome?

<p>4.2 × 10^6 (B)</p> Signup and view all the answers

How do mRNA and tRNA molecules interact on ribosomes?

<p>To synthesize proteins from mRNA templates (C)</p> Signup and view all the answers

What describes the stability of ribosomes in the cytoplasm during translation?

<p>Quite stable and capable of many translation cycles (B)</p> Signup and view all the answers

What is the primary function of ribosomes in the cell?

<p>To synthesize proteins (A)</p> Signup and view all the answers

Flashcards

DNA Replication

The process of creating two identical DNA molecules from one original DNA molecule.

Double Helix

The twisted ladder-like structure of DNA.

Base Pairs

Adenine (A) with Thymine (T), and Guanine (G) with Cytosine (C).

DNA

A molecule that carries genetic instructions for living organisms.

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Watson-Crick Model

A model depicting DNA's double helix structure.

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Biological Functions of DNA

DNA's roles in living organisms (e.g., storing, carrying genetic information).

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DNA Polymerase

An enzyme that plays a role in DNA replication.

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Antiparallel Strands

Two DNA strands running in opposite directions.

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PCR components

PCR needs a DNA template, primers, nucleotides, buffer, Mg ions, and a heat-stable DNA polymerase (like Taq polymerase).

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PCR primers

Short DNA sequences that bind to specific target DNA regions, defining the area to copy.

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DNA template

Original DNA molecule used as a pattern to create new DNA copies.

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DNA transcription

The process of creating RNA from a DNA template.

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Transcription stages

DNA transcription happens in three steps: initiation, elongation, and termination.

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mRNA Function

mRNA molecules carry genetic information from DNA to the ribosomes, where proteins are synthesized.

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mRNA Structure

mRNA has a 5' cap (7-methylguanosine triphosphate) and a 3' poly(A) tail.

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5' Cap Function

The 5' cap helps in the recognition of mRNA by the translation machinery and protects it from degradation.

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Poly(A) Tail Function

The poly(A) tail at the 3' end improves stability and prevents degradation of mRNA.

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mRNA Heterogeneity

mRNA molecules vary greatly in size and stability.

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Coding & Template Strands

The coding strand of DNA has the same sequence as the mRNA, except with T replaced by U. The template strand is used to create mRNA.

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mRNA Isolation

Poly(A) tails can be used to separate mRNA from other RNA molecules.

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mRNA Processing

A series of modifications that convert hnRNA into mature messenger RNA (mRNA) before it exits the nucleus.

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Poly-A Tail

A long chain of adenine nucleotides added to the end (3' end) of mRNA, stabilizing it and helping it exit the nucleus.

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Translation

The process of converting the genetic information in mRNA into a specific sequence of amino acids, forming a protein.

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Ribosome

A cellular organelle that reads mRNA and assembles amino acids into proteins.

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Genetic Code

The set of rules that determines the sequence of amino acids coded for by each mRNA codon.

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Translation Phases

Translation, the process of creating proteins from mRNA, occurs in three phases: initiation, elongation, and termination.

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Initiation (Translation)

The ribosome, a protein-making machine, binds to the mRNA and the first tRNA carrying the start codon.

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Elongation (Translation)

The ribosome reads each codon on the mRNA, adding the corresponding amino acid to the growing polypeptide chain.

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Termination (Translation)

The ribosome reaches a stop codon on the mRNA and releases the complete polypeptide. The ribosome then moves on to translate the next message.

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tRNA Diversity

There are at least 20 different types of tRNAs, one for each of the 20 amino acids needed for protein synthesis.

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tRNA Stability

tRNA molecules are more stable in prokaryotes compared to eukaryotes.

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mRNA Stability: Prokaryotes vs. Eukaryotes

In prokaryotes, mRNA molecules are relatively unstable and degrade quickly. However, in eukaryotes, mRNA is generally more stable and persists for a longer period.

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Aminoacyl tRNA Structure

A typical aminoacyl tRNA has the amino acid attached to the 5' CCA terminal. It contains an anticodon loop, T, C, and dihydrouracil (D) arms, all connected by intramolecular hydrogen bonding.

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Ribosome: Protein Synthesis Machinery

A ribosome is a cellular structure composed of RNA and proteins, acting as a 'machine' for protein synthesis. mRNA and tRNA interact on the ribosome to translate genetic information into amino acid sequences.

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Polysome: Multiple Ribosomes on One mRNA

In active protein synthesis, multiple ribosomes can bind to a single mRNA molecule, forming a complex called a polysome. This allows for efficient production of many protein copies from one mRNA template.

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Mammalian Ribosome: 80S Structure

Mammalian ribosomes have a sedimentation velocity of 80S (Svedberg units) and comprise two subunits: a larger 60S subunit and a smaller 40S subunit.

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Ribosome Subunit Components: 60S

The larger 60S subunit contains a 5S rRNA, a 5.8S rRNA, and a 28S rRNA, along with multiple polypeptide chains.

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Ribosome Subunit Components: 40S

The smaller 40S subunit contains a single 18S rRNA and about 30 polypeptide chains.

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Ribosomal rRNA Synthesis and Maturation

All ribosomal RNA molecules except the 5S rRNA are processed from a larger precursor RNA molecule (45S) in the nucleolus. The 5S rRNA is transcribed separately. Following methylation, these rRNAs associate with specific ribosomal proteins.

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Study Notes

Biochemistry I - Biological Functions of DNA

  • DNA Replication: The process of producing two identical DNA molecules from one original, essential for cell division and repair.
  • DNA Replication Stages: Initiation, unwinding, primer synthesis, and elongation.
  • DNA Replication Details: Occurs in almost all living organisms, ensuring each cell receives a copy of the DNA.

DNA Structure

  • Model: Watson and Crick double-helical structure of B-form DNA
  • Double Helix Dimensions: Width 20 Å, vertical distance spanned by one complete turn 34 Å. A complete turn includes 10 base pairs (bp), so the rise is 3.4 Å per bp.
  • Polarity: Antiparallel strands (short arrows).
  • Grooves: Major and minor grooves depicted for visualization.
  • Components: Adenine (A), Cytosine (C), Guanine (G), Thymine (T), phosphate, and deoxyribose sugar.

DNA Biological Functions

  • Genetic Information Storage: DNA stores instructions for building proteins and the genes necessary for cellular function.
  • Protein Synthesis: Information is used to create proteins.
  • Inheritance: DNA provides the genetic information passed on to offspring.
  • Transcription: Copying a segment of DNA into RNA (like mRNA).
  • Translation: Converting the mRNA code into amino acids to form proteins.
  • Replication: Making identical copies of DNA.

PCR (Polymerase Chain Reaction)

  • Technique: Laboratory method for rapidly copying DNA segments millions to billions of times.
  • Process Steps: Denaturation (separating strands), Annealing (primers binding), and Extension (new strand creation).
  • Materials: Primers, DNA polymerase, nucleotides (dNTPs), and buffer.
  • Applications: Amplifying specific DNA segments for further study or analysis.

DNA Transcription

  • Process: The creation of single-stranded RNA (mRNA) from a strand of DNA.
  • Location: Occurs in cells' nuclei (for eukaryotic organisms).
  • Stages: Initiation, elongation, and termination.
  • Mechanism: RNA polymerase synthesizes RNA using the DNA strand as a template with the bases T being replaced by U.
  • Modifications: Additions (like a cap) can occur to mRNA after its creation.
  • Implications: Critical step in gene expression to create proteins coded by DNA.

DNA Translation

  • Process: Translating mRNA codons into the sequence of amino acids forming a polypeptide chain.
  • Location: Primarily at the ribosomes in cells' cytoplasm.
  • Mechanism: tRNA brings amino acids according to the mRNA code.
  • Polypeptide Synthesis: The ribosomes assemble amino acids brought by tRNA to create the polypeptide chain.
  • Phases: Initiation, elongation, and termination.

Messenger RNA (mRNA)

  • Role: Carries genetic information from DNA to ribosomes.
  • Structure: Heterogeneous in size, but generally shorter than DNA.
  • Specific Characteristics: Often modified at the 5' end (capped), and often modified at the 3' end with a poly(A) tail (especially in eukaryotes).
  • **Stability:**mRNA stability varies across organisms and between mRNA types

Transfer RNA (tRNA)

  • Characteristics: Carries specific amino acids required for protein synthesis.
  • Structure: A variety of sizes (typically 74 to 95 nucleotides) and a secondary structure resembling a cloverleaf.
  • Function: Adaptor between mRNA and amino acids, critical for protein synthesis.
  • Importance: Essential to bringing amino acids to the ribosomes

Ribosomal RNA (rRNA)

  • Structure: Component of ribosomes, essential to protein synthesis.
  • Function: Forms structural core of ribosomes, crucial to assembly of ribosomes, and important in the mechanism of protein synthesis.
  • Components: Ribosome's structural core and many polypeptides (more than 50) in the ribosome

Recombinant DNA Technology

  • Process: Combining DNA fragments from different organisms to produce something new.
  • Steps: Isolating the target gene, carrying DNA, and introducing the constructed DNA into a host organism to express the protein of interest.
  • Applications: Creating new proteins or improving traits in organisms.

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Biological Functions of DNA 2024-2025 PDF

Description

Explore the fundamental biological functions of DNA in this quiz covering DNA replication and structure. Understand the key stages of replication and the structural components that define the double helix. Test your knowledge on how DNA stores genetic information essential for life.

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