Molecular Biology: Cells and Central Dogma

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Questions and Answers

What is the primary role of the plasma membrane in cells?

Synthesizing proteins

Storing hereditary information

Facilitating communication between cells

Regulating the passage of nutrients and waste (correct)

Which statement accurately reflects the central dogma of molecular biology?

Information flows in one direction, from DNA to RNA to protein (correct)

Information is stored in proteins for replication

Information flows from protein to RNA to DNA

Information flows from RNA to DNA to protein

What is responsible for the replication of hereditary information in cells?

Cellular respiration

Template polymerization (correct)

Protein synthesis

Translation of RNA

Which molecular processes are common to all cells?

Transcription and translation Signup and view all the answers

What defines the diverse characteristics of different cell types?

Shape, size, movement, and metabolism Signup and view all the answers

How is molecular biology primarily described?

The intersection of genetics and biochemistry Signup and view all the answers

Which of the following functions is NOT performed by all cells?

Synthesizing lipids Signup and view all the answers

What is the key feature of cellular communication highlighted in the content?

Intricate systems connecting cells Signup and view all the answers

What characteristic distinguishes eukaryotic mRNA from prokaryotic mRNA?

Eukaryotic mRNA is monocistronic. Signup and view all the answers

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

To provide stability to the mRNA molecule. Signup and view all the answers

What are the three distinct parts of a nucleotide?

Phosphate group, nitrogenous base, and pentose sugar Signup and view all the answers

What are introns in eukaryotic hnRNA?

Noncoding regions that must be removed. Signup and view all the answers

What type of sugar is found in RNA nucleotides?

Ribose Signup and view all the answers

Which of the following statements about prokaryotic mRNA is correct?

Prokaryotic mRNA is polycistronic. Signup and view all the answers

How do the hydroxyl groups in phosphoric acid influence the charge of nucleotides?

They become negatively charged upon losing H+ ions Signup and view all the answers

What is the role of ribosomes in protein synthesis?

They are the site of protein synthesis. Signup and view all the answers

What differentiates deoxyribose from ribose?

Deoxyribose lacks a hydroxyl group at C2' Signup and view all the answers

What is the nature of nucleic acids based on their components?

They are acidic due to their phosphate groups Signup and view all the answers

Which of the following correctly describes the nitrogenous bases in nucleotides?

They are classified into two classes based on aromatic rings Signup and view all the answers

What charge do nucleotides acquire due to their phosphate group under physiological conditions?

Negatively charged Signup and view all the answers

The pentose sugar in nucleic acids is named for which characteristic?

It is a five-carbon sugar Signup and view all the answers

What are the components of a nucleotide?

Ribose, nitrogenous base, and phosphate group Signup and view all the answers

Which nitrogenous bases are classified as pyrimidines?

Thymine, Uracil, and Cytosine Signup and view all the answers

How are nucleosides named when containing a purine base?

By adding 'osine' to the base name Signup and view all the answers

Which of the following correctly represents a nucleoside in DNA?

2' deoxycytidine (dC) Signup and view all the answers

What is the bond formed between the phosphate group and the sugar in a nucleotide?

Ester bond Signup and view all the answers

How many carbon and nitrogen atoms are present in a pyrimidine aromatic ring?

4 carbons and 2 nitrogens Signup and view all the answers

Which of the following is a nucleoside in RNA?

Uridine (U) Signup and view all the answers

What prefix is added to the name of nucleosides when the sugar is deoxyribose?

Deoxy Signup and view all the answers

What type of sequence allows for the formation of triple helices in DNA?

Polypyrimidine sequences Signup and view all the answers

Which DNA structure is primarily formed by a sequence of alternating T and C residues?

H-DNA Signup and view all the answers

What is the effect of negative supercoiling on DNA?

Facilitates unwinding of the double helix Signup and view all the answers

How do topoisomerases affect DNA supercoiling?

They have both nuclease and ligase activity Signup and view all the answers

What is the consequence of positive DNA supercoils?

Makes opening the helix more difficult Signup and view all the answers

What does a sharp bend in DNA structure indicate?

Formation of a triple helix Signup and view all the answers

Which type of sequences can create unusual structures leading to gene regulation?

Mirror repeat sequences Signup and view all the answers

What is a function of the superhelices formed by negative DNA supercoiling?

To facilitate gene expression Signup and view all the answers

Study Notes

Cells: Universal Features and Differences

All cells are enclosed in a plasma membrane.
All cells store genetic information as a linear chemical code.
All cells replicate genetic information through template polymerization.
All cells transcribe genetic information into RNA.
All cells translate RNA into proteins through the same mechanism.
All cells use proteins as catalysts.

Cell Differences

Cells differ in shape, size, movement, lability, metabolism, and lifestyle.
Cell classification is based on rRNA sequences.

Molecular Biology: Introduction

Molecular Biology focuses on the formation, structure, and function of macromolecules essential for life.
It emphasizes the role of nucleic acids and proteins in cell replication and genetic information transmission.
It emerged from the intersection of genetics and biochemistry.

Central Dogma

Genetic information flows in one direction: DNA to RNA to protein.
RNA can directly code for protein as well.

Nucleic Acids: Chemical Composition

Nucleic acids are polymers of nucleotides.
Nucleotides consist of a pentose sugar, a nitrogenous base, and a phosphate group.

Nucleotides: Components

Phosphate group: Inorganic phosphate (Pi) or phosphoric acid (H3PO4), negatively charged in cells.
Sugar: Pentose with five carbon atoms (1'-5').
- Ribose: Present in RNA molecules.
- Deoxyribose: Present in DNA molecules, lacks a hydroxyl group at the 2' carbon.
Nitrogenous bases: Aromatic molecules classified into:
- Purines: Contain a purine ring (pyrimidine and imidazole rings) - Adenine (A) and Guanine (G).
- Pyrimidines: Contain a pyrimidine ring (four carbons and two nitrogens) - Thymine (T), Uracil (U), and Cytosine (C).

Nucleosides: Nomenclature

A nucleoside is formed by the binding of a sugar to a nitrogenous base via a N-glycosidic bond.
Names are formed by adding "idine" to pyrimidines or "iosine" to purines.
Deoxyribose nucleosides: Prefix "deoxy" added.
DNA nucleosides: 2' deoxyadenosine (dA), 2' deoxyguanosine (dG), 2' deoxycytidine (dC), and 2' deoxythymidine (dT).

Nucleotides: Formation and Nomenclature

Nucleotides are formed by esterification of a phosphate group to the 5' hydroxyl group of a nucleoside.
Nucleotides are called nucleoside monophosphates.
DNA components: dAMP, dGMP, dTMP, and dCMP.
RNA components: AMP, GMP, UMP, and CMP.

Palindromes and Polypyrimidine/Polypurine Sequences

Sites recognized by DNA-binding proteins in DNA are often arranged as palindromes.
Polypyrimidine or polypurine sequences can form triple helices or H-DNA, playing a role in gene regulation.

Unusual DNA Tertiary Structures: H-DNA

Alternating T and C sequences can form a mirror repeat centered on a T or C.
The pyrimidine strand forms a triple helix with the other half of the repeat.
The purine strand remains unpaired, resulting in a sharp bend in the DNA.

DNA Structures

Double-stranded helix with two antiparallel strands.
Sugar-phosphate backbone on the outside, bases inside.
Bases are paired by hydrogen bonds: A with T, G with C.

Supercoiling of DNA

Negative supercoiling:
- Energetically favored.
- Facilitates unwinding of the double helix for replication, recombination, and transcription.
Positive supercoiling:
- Makes opening the helix more difficult.

Topoisomerases

Enzymes with nuclease and ligase activity.
Change the amount of supercoiling in DNA.

mRNA: Prokaryotic vs. Eukaryotic

Prokaryotic mRNA: Polycistronic, encoding multiple polypeptides.
Eukaryotic mRNA: Monocistronic, encoding one protein.
- Synthesized in the nucleus as hnRNA (heterogeneous nuclear RNA).
- Contains noncoding introns and coding exons.
- Introns are spliced out before translation.
- Poly (A) tail of 100-200 adenylic acid residues at the 3' end, promoting stability.

rRNA

Ribosomal RNA, about 65% of ribosomes.
Ribosomes are supramolecular assemblies where protein synthesis occurs.

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Description

Explore the universal features of cells and their differences in morphology and function. This quiz delves into the fundamental principles of molecular biology, including the central dogma of molecular biology, mechanisms of genetic information transmission, and the role of macromolecules. Test your knowledge on how cells replicate and utilize genetic information!