Chapter 4 – Questions

These flashcards review major principles from Chapter 4, covering DNA/RNA structure, gene definitions, genetic code, protein synthesis, chromatin organization, gene regulation, DNA replication, and the cell cycle.

Who first isolated what we now call DNA and coined the term “nuclein”?

Johann Friedrich Miescher

What three components make up a single nucleotide of DNA?

A deoxyribose sugar, a phosphate group, and a nitrogenous base

Which nitrogenous bases are purines?

Adenine (A) and Guanine (G)

Which nitrogenous bases are pyrimidines in DNA?

Cytosine (C) and Thymine (T)

What shape best describes the overall structure of DNA?

A double helix resembling a spiral staircase

How many hydrogen bonds unite adenine with thymine?

Two hydrogen bonds

How many hydrogen bonds unite cytosine with guanine?

Three hydrogen bonds

State the Law of Complementary Base Pairing.

The nucleotide sequence of one DNA strand dictates the complementary sequence of the other (A pairs with T, C pairs with G).

Define a gene in modern terms.

An information-containing segment of DNA that codes for a molecule of RNA which, in turn, plays a role in synthesizing one or more proteins.

Approximately what percentage of human DNA is noncoding?

About 98% of total DNA is noncoding

What is a genome?

All the DNA in one complete set of 23 chromosomes

How many genes does a human genome roughly contain?

About 20,000 genes

What is genomics?

The study of the entire genome and how genes and non-coding regions interact to influence structure and function

Name the three major types of RNA involved in protein synthesis.

Messenger RNA (mRNA), Ribosomal RNA (rRNA), and Transfer RNA (tRNA)

Which base replaces thymine in RNA?

Uracil (U)

What is a base triplet?

A sequence of three DNA nucleotides that codes for one amino acid

What is a codon and where is it found?

A three-base sequence on mRNA that specifies an amino acid or stop signal

Which codon serves as the universal start codon and what amino acid does it code for?

AUG; it codes for methionine

Name the three stop codons.

UAG, UGA, and UAA

In which cellular compartment does transcription occur?

The nucleus

Which enzyme is primarily responsible for synthesizing mRNA during transcription?

RNA polymerase

What are introns?

Noncoding segments of pre-mRNA that are removed before translation

What is alternative splicing?

A process that joins exons in different combinations, allowing a single gene to code for multiple proteins

Where does translation occur?

In the cytoplasm on ribosomes (free or attached to rough ER)

What is an anticodon?

A three-nucleotide sequence on tRNA complementary to an mRNA codon

During translation, what are the three basic stages?

Initiation, Elongation, and Termination

What is a polyribosome?

A single mRNA molecule simultaneously bound by multiple ribosomes

What role do chaperone proteins play?

They guide the folding of newly synthesized proteins and help refold stress-damaged proteins

Where are proteins destined for secretion or lysosomes synthesized?

On ribosomes bound to the rough endoplasmic reticulum

Which coat protein helps shape and select cargo in transport vesicles leaving the ER?

Clathrin

What is the effect of prolactin on mammary gland cells at the genetic level?

It activates the casein gene, increasing casein mRNA transcription and protein secretion for milk production

Explain semiconservative DNA replication.

Each daughter DNA molecule consists of one original (parental) strand and one newly synthesized strand

Name the four basic steps of DNA replication.

Unwinding, Unzipping, Building new strands, and Repackaging

Which enzyme unwinds the DNA double helix during replication?

DNA helicase

Which enzyme links short DNA fragments on the lagging strand?

DNA ligase

How accurate is DNA polymerase after proofreading?

Approximately one error per one billion nucleotides

List the three subphases of interphase.

G1 (First Gap), S (Synthesis), and G2 (Second Gap)

What happens during the S phase of the cell cycle?

DNA replication and duplication of centrioles

Define the G0 phase.

A phase in which cells exit the cell cycle and cease dividing for an extended period or permanently

What are the four main stages of mitosis?

Prophase, Metaphase, Anaphase, and Telophase

During which mitotic phase do chromosomes align on the equator of the cell?

Metaphase

What significant event characterizes anaphase?

Sister chromatids separate and move toward opposite poles

How is cytokinesis achieved in animal cells?

Myosin pulls on actin filaments, creating a cleavage furrow that pinches the cell in two

What is contact inhibition?

The cessation of cell division when cells come into close contact with neighboring cells

Describe a nucleosome.

A core of eight histone proteins with DNA wrapped around it and a linker DNA segment connecting adjacent cores

What is a chromosome territory?

A distinct region of the nucleus occupied by an individual chromosome

What protein structure on chromatids serves as the attachment site for spindle fibers?

The kinetochore

What is genomic medicine?

Application of genome knowledge to predict, diagnose, and treat disease

Name two examples of hereditary disorders mentioned in the lecture that involve single-gene defects.

Cystic fibrosis and hemophilia (others include color blindness, diabetes mellitus)

How long is the average human DNA molecule?

About 2 inches (≈5 cm)

What is the proteome?

The entire set of proteins produced by an organism

How can one gene code for many different proteins?

Through mechanisms such as alternative splicing and post-translational modifications

Give an example of a non-protein compound whose synthesis is under indirect genetic control.

Testosterone (synthesized from cholesterol via enzyme-mediated steps)

What is a sister chromatid?

One of two identical DNA strands joined at a centromere after DNA replication

What triggers the start of transcription on DNA?

Promoter (start) sequences recognized by RNA polymerase

Why are chromosomes highly condensed during prophase?

Condensation makes them easier to separate and distribute to daughter cells

What are growth factors?

Chemical signals that stimulate cells to divide

What is the function of histones?

They package and organize DNA into chromatin

Why don’t all cells express all their genes?

Gene regulation allows cells to turn genes on or off based on function, time, and environmental signals

What are single-nucleotide polymorphisms (SNPs)?

Single-base variations in the genome that contribute to human genetic diversity

Which type of RNA is capped for ribosome recognition?

Messenger RNA (mRNA)

Which enzyme corrects DNA replication errors?

DNA polymerase via its proofreading capability