Biology and Chemistry Basics Quiz

Central Dogma of Molecular Biology

This is the process by which a gene's information is converted into the structures and functions of a cell
The process involves producing a biologically functional molecule of either protein or RNA (gene product)
Gene expression involves the controlled sequence of events leading to protein synthesis

Learning Objectives

Identifying the learning objectives in various sections of the presentation

DNA Structure and Replication

DNA is a polymer of nucleotides. Deoxyribonucleic acid (DNA) is made of two strands of nucleotides.
DNA forms a double helix and stores hereditary information.
DNA replication is a process where the genome is duplicated by DNA polymerase and primers. Semidiscontinuous replication is used where each strand of the parental DNA is used as a template to make the new daughter strand.
DNA replication produces two complete double helices, each with one old and one new strand.

DNA Structure Determination

Rosalind Franklin collected X-ray diffraction data in the 1950s.
Watson and Crick proposed a 3D model of DNA.

DNA Repair Mechanisms

DNA polymerase proofreading, direct repair, base excision repair, nucleotide excision repair, mismatch repair, and recombination are mechanisms for DNA repair.

Gene Expression and Transmission of Genetic Information

The process where a gene's information is transformed into structures and functions of a cell is called gene expression.
Gene expression involves producing biologically functional molecules— either proteins or RNA.

Nucleic Acid Function

DNA carries genetic information in the form of its nucleotide sequence
DNA is transcribed into mRNA, which is translated into a sequence of amino acids.

Transcription Overview

RNA is transcribed from DNA templates. Enzymes involved are RNA polymerases.
RNA polymerase reactions are driven by two factors: the conversion of a 5´ α-nucleotide phosphate from a phosphate anhydride form to a phosphodiester bond, and the release of pyrophosphate.
Transcription initiation involves RNA polymerase binding to the promoter region of a gene and unwinding DNA.
During elongation, RNA polymerase reads the template strand and adds complementary ribonucleotides.
Termination of RNA polymerase occurs when it hits a stop signal (prokaryotes) or falls off (eukaryotes).

RNA Processing

Before translation in eukaryotes, RNA is processed.
Prokaryotes do not require any processing.
Pre-mRNA is renamed to mRNA once it has been processed.
Pre-mRNA processing is done through 3 steps: adding a modified nucleotide 5' cap, a poly-A tail at the 3' end, and splicing out exons.
Modifications assist in mRNA export, protect against enzymes, and facilitate ribosome attachment.

mRNA Splicing

Most eukaryotic genes and transcripts have long non-coding stretches.
The non-coding regions are called introns.
The other regions are called exons, involved in eventually expressed and translated into amino acid sequences.
RNA splicing removes introns and joins exons to create a continuous coding sequence.

Translation

Translation involves the synthesis of proteins from mRNA. This is a 3-step process.
Initiation, Elongation and Termination

Polyribosomes

Many ribosomes can attach to one mRNA at once to enable fast translation of multiple copies of the protein.

Control of Gene Expression

Transcriptional control, RNA processing control, RNA transport control, mRNA degradation control, initiation of translation control, and post-translational modifications

Mistakes During Replication

Base pairing rules—the correct pairings must be maintained
Correct pairings fit the polymerase active sites
If incorrect nucleotides are included, DNA polymerase uses its proofreading ability to cleave the phosphodiester bond of improper nucleotide.
It then continues down the 5´ to 3´ direction

Mutagens

Spontaneous mutations can occur during DNA replication, recombination, or repair.
Mutagens are physical or chemical agents that induce mutations.
Carcinogens cause cancer. Heterocyclic amines are produced when meat is charred. Nitrosamines are used in preserving meat. Cigarette smoke contains known carcinogens like Benzopyrene diol epoxide.
Point mutations can result from substitution mutations, where one purine is replaced by another purine, and a transversion, where a purine is replaced by a pyrimidine or vice versa. Other mutations can result from insertions and deletions of one or more nucleotide pairs.

DNA Repair

DNA polymerase proofreading, nucleotide excision repair, base excision repair, mismatch repair, and transcription-coupled repair are categorized as DNA repair mechanisms.

Cancer

Cell division and apoptosis resistance are crucial for a cancer cell.
Proto-oncogenes can be converted to oncogenes through activating mutations.
Unregulated cell division or resistance to apoptosis can lead to cancerous effects.
Malignant cancer cells display cellular immortality and can induce angiogenesis and metastasize.

Other

The central dogma describes the flow of genetic information from DNA to RNA to protein.
Learning objectives are frequently given with relevant slides in the presentation.