Molecular Biology - DNA, RNA, & Protein Synthesis Flashcards

Question 1

What is the Central Dogma of Molecular Biology?

Accepted Answer

The fundamental principle that genetic information flows from DNA to RNA to protein, describing the basic sequence of information transfer in living organisms.

Question 2

Describe the three components of a DNA nucleotide.

Accepted Answer

A deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), or Thymine (T).

Question 3

What type of bond links nucleotides together to form a single DNA or RNA strand?

Accepted Answer

A phosphodiester bond, formed between the phosphate group of one nucleotide and the $3'$ hydroxyl group of the sugar of the next nucleotide.

Question 4

How do DNA and RNA sugars differ?

Accepted Answer

DNA contains deoxyribose, which lacks an oxygen atom at the $2'$ carbon, while RNA contains ribose, which has a hydroxyl group (-OH) at the $2'$ carbon.

Question 5

What are the base pairing rules in a DNA double helix?

Accepted Answer

Adenine (A) pairs with Thymine (T) via two hydrogen bonds, and Guanine (G) pairs with Cytosine (C) via three hydrogen bonds. This is known as Chargaff's rules.

Question 6

List three key structural differences between DNA and RNA.

Accepted Answer

DNA is typically a double helix, contains deoxyribose sugar, and uses Thymine (T). RNA is typically single-stranded, contains ribose sugar, and uses Uracil (U) instead of Thymine.

Question 7

What is the primary function of DNA helicase in DNA replication?

Accepted Answer

DNA helicase unwinds and separates the two strands of the DNA double helix by breaking the hydrogen bonds between complementary base pairs, creating a replication fork.

Question 8

Explain the role of DNA polymerase III in DNA replication.

Accepted Answer

DNA polymerase III synthesizes new DNA strands by adding nucleotides complementary to the template strand in the $5' ightarrow 3'$ direction. It also possesses $3' ightarrow 5'$ exonuclease activity for proofreading.

Question 9

What are Okazaki fragments and on which strand are they formed?

Accepted Answer

Okazaki fragments are short, newly synthesized DNA fragments that are formed discontinuously on the lagging strand during DNA replication. They are later joined together by DNA ligase.

Question 10

What is the function of DNA ligase during replication?

Accepted Answer

DNA ligase joins the Okazaki fragments on the lagging strand, as well as any nicks in the DNA backbone, by forming phosphodiester bonds between adjacent nucleotides.

Question 11

Define transcription and identify the key enzyme involved.

Accepted Answer

Transcription is the process of synthesizing an RNA molecule from a DNA template. The key enzyme responsible for this process is RNA polymerase.

Question 12

What is a promoter region in the context of transcription?

Accepted Answer

A promoter is a specific DNA sequence located upstream of a gene that serves as a binding site for RNA polymerase and transcription factors, initiating gene transcription.

Question 13

Describe the function of enhancers in gene expression.

Accepted Answer

Enhancers are DNA sequences that can be located far from a gene (upstream, downstream, or within an intron) and bind to activator proteins, significantly increasing the rate of transcription of a gene.

Question 14

What post-transcriptional modifications occur in eukaryotic mRNA?

Accepted Answer

Eukaryotic mRNA undergoes $5'$ capping (addition of a modified guanine nucleotide), $3'$ polyadenylation (addition of a poly-A tail), and splicing (removal of introns and joining of exons).

Question 15

Define translation and identify the cellular machinery responsible.

Accepted Answer

Translation is the process by which the genetic information encoded in mRNA is used to synthesize a polypeptide chain (protein). Ribosomes are the cellular machinery responsible for translation.

Question 16

What is the role of tRNA in translation?

Accepted Answer

Transfer RNA (tRNA) molecules act as adaptors, carrying specific amino acids to the ribosome and recognizing corresponding codons on the mRNA template via their complementary anticodon loop.

Question 17

Explain what a codon is and how the genetic code is described as 'degenerate.'

Accepted Answer

A codon is a three-nucleotide sequence on mRNA that specifies a particular amino acid or a stop signal. The genetic code is degenerate because most amino acids are specified by more than one codon.

Question 18

What are the start and stop codons in the genetic code?

Accepted Answer

The start codon is AUG, which codes for Methionine (Met) and initiates translation. The three stop codons are UAA, UAG, and UGA, which signal the termination of translation.

Question 19

Briefly describe the concept of an operon in prokaryotic gene regulation.

Accepted Answer

An operon is a functional unit of DNA in prokaryotes containing a cluster of genes under the control of a single promoter and operator, allowing for coordinated gene expression in response to environmental cues.

Question 20

How does the Lac operon exemplify inducible gene regulation?

Accepted Answer

The Lac operon is inducible; it is typically 'off' but can be turned 'on' in the presence of lactose (the inducer). Lactose binds to the repressor protein, preventing it from binding to the operator and allowing transcription.

Question 21

What is epigenetics, and how does DNA methylation relate to it?

Accepted Answer

Epigenetics refers to heritable changes in gene expression that occur without altering the underlying DNA sequence. DNA methylation, the addition of a methyl group to cytosine bases, often leads to gene silencing by blocking transcription factor binding or recruiting repressive proteins.

Question 22

How do histone modifications influence gene expression?

Accepted Answer

Histone modifications (e.g., acetylation, methylation, phosphorylation) alter the chromatin structure, making DNA more or less accessible to transcription machinery. For example, histone acetylation generally loosens chromatin, promoting gene expression, while some histone methylations can lead to compaction and repression.

Molecular Biology - DNA, RNA, & Protein Synthesis

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