2. Membrane physiology & Contraction of skeletal muscle

Question 1

The nucleus is considered the “control center” of the cell because it primarily regulates what cellular process?

Gene expression through regulation of protein synthesis.

Question 2

Which molecule serves as the permanent genetic blueprint of the cell?

DNA (Deoxyribonucleic acid).

Question 3

What is the functional unit of heredity?

Gene.

Question 4

A gene ultimately determines the structure of what biological molecule?

Protein.

Question 5

Why can two different cell types contain identical DNA but perform completely different functions?

Different genes are expressed (turned on or off) in each cell.

Question 6

Which process copies genetic information from DNA into RNA?

Transcription.

Question 7

Which process converts the nucleotide sequence of mRNA into an amino acid sequence?

Translation.

Question 8

Where does transcription occur?

Inside the nucleus.

Question 9

Where does translation occur?

On ribosomes in the cytoplasm or rough endoplasmic reticulum.

Question 10

Which RNA carries genetic information from the nucleus to ribosomes?

Messenger RNA (mRNA).

Question 11

Which RNA transports amino acids to the ribosome?

Transfer RNA (tRNA).

Question 12

Which RNA forms the structural and catalytic component of ribosomes?

Ribosomal RNA (rRNA).

Question 13

A mutation changes one nucleotide in DNA. Which process is affected first?

Transcription.

Question 14

During translation, what portion of mRNA determines one amino acid?

Codon.

Question 15

A codon consists of how many nucleotides?

Three.

Question 16

What is the complementary sequence found on tRNA called?

Anticodon.

Question 17

During protein synthesis, which molecule directly recognizes the codon?

tRNA anticodon.

Question 18

Which organelle serves as the site of protein synthesis?

Ribosome.

Question 19

What is the major function of rough endoplasmic reticulum?

Synthesis of secreted, membrane, and lysosomal proteins.

Question 20

Why are ribosomes attached to rough ER?

To synthesize proteins destined for secretion or membrane insertion.

Question 21

Proteins synthesized on free ribosomes usually remain where?

Within the cytoplasm.

Question 22

What is the start codon for protein synthesis?

AUG (codes for methionine).

Question 23

Which amino acid is encoded by the start codon AUG?

Methionine.

Question 24

Which codons terminate translation?

UAA, UAG, and UGA.

Question 25

Why are stop codons called “nonsense codons”?

They do not code for any amino acid.

Question 26

What enzyme synthesizes RNA during transcription?

RNA polymerase.

Question 27

Which DNA strand serves as the template during transcription?

Template (antisense) strand.

Question 28

What is the function of the promoter region?

It serves as the binding site for RNA polymerase to initiate transcription.

Question 29

Which promoter sequence is commonly recognized in eukaryotic cells?

TATA box.

Question 30

What would most likely happen if the promoter region were deleted?

Transcription would not begin.

Question 31

What is meant by gene expression?

Production of a functional protein from a gene.

Question 32

What is differential gene expression?

Selective activation of specific genes in different cell types.

Question 33

Which molecule can inhibit protein synthesis by binding complementary mRNA?

MicroRNA (miRNA).

Question 34

How does miRNA decrease protein production?

By preventing translation or promoting degradation of mRNA.

Question 35

Which RNA is commonly used experimentally to silence gene expression?

Small interfering RNA (siRNA).

Question 36

Which process ensures that genetic information is copied before cell division?

DNA replication.

Question 37

When during the cell cycle does DNA replication occur?

S phase of interphase.

Question 38

Which enzyme synthesizes new DNA strands?

DNA polymerase.

Question 39

Which enzyme joins DNA fragments during replication?

DNA ligase.

Question 40

What are Okazaki fragments?

Short DNA fragments synthesized on the lagging strand.

Question 41 What is the purpose of ribosomal RNA in the ribosome?

It forms about 60% of the ribosome and helps provide the structure needed for protein synthesis.

Question 42 What is the main role of transfer RNA during translation?

It transports specific amino acids to the ribosome and matches anticodons with mRNA codons.

Question 43 What is the role of messenger RNA in protein synthesis?

It carries the genetic code from DNA to the ribosome and determines the amino acid sequence of the protein.

Question 44 Why are ribosomes considered the “manufacturing plant” of protein synthesis?

Because they read mRNA and assemble amino acids into proteins.

Question 45 Where are ribosomal RNA genes located?

In five pairs of chromosomes.

Question 46 What is the nucleolus?

A specialized nuclear structure where ribosomal RNA is processed and ribosomal subunits are assembled.

Question 47 Why is the nucleolus large in protein-producing cells?

Because those cells synthesize large amounts of ribosomal RNA.

Question 48 Can proteins be formed inside the nucleus?

No. Mature ribosomes are not present in the nucleus, so protein synthesis occurs in the cytoplasm.

Question 49 What is microRNA?

A short noncoding RNA that regulates gene expression.

Question 50 How does microRNA decrease gene expression?

By binding to complementary RNA and repressing translation or causing mRNA degradation.

Question 51 What is small interfering RNA?

A short double-stranded RNA that blocks expression of specific genes.

Question 52 What is the function of the RNA-induced silencing complex (RISC)?

It mediates gene silencing by blocking translation or promoting mRNA degradation.

Question 53 What is translation?

The formation of proteins on ribosomes using mRNA as the template.

Question 54 What happens when a stop codon enters the ribosome?

Protein synthesis ends and the protein is released into the cytoplasm.

Question 55 What is a polyribosome?

A cluster of ribosomes translating the same mRNA at the same time.

Question 56 Why are polyribosomes important?

They allow rapid formation of multiple protein copies from one mRNA molecule.

Question 57 What is the first chemical step in amino acid activation during protein synthesis?

ATP combines with the amino acid to form an amino acid–AMP complex.

Question 58 What happens after amino acid activation?

The activated amino acid binds to its specific tRNA.

Question 59 What happens when the amino acid–tRNA complex reaches the ribosome?

The anticodon of tRNA temporarily binds to the complementary codon on mRNA.

Question 60 What enzyme forms peptide bonds between amino acids?

Peptidyl transferase.

Question 61 How many high-energy phosphate bonds are used for each amino acid added to a growing protein chain?

Four.

Question 62 Why is protein synthesis considered one of the most energy-consuming processes in the cell?

Because each amino acid added requires multiple high-energy phosphate bonds.

Question 63 What is peptide linkage?

The bond formed when the carboxyl group of one amino acid joins the amino group of another, releasing water.

Question 64 What do protein enzymes formed by ribosomes do in the cell?

They control synthesis of lipids, glycogen, purines, pyrimidines, and many other substances.

Question 65 What are the two main mechanisms by which biochemical activity in the cell is controlled?

Genetic regulation and enzyme regulation.

Question 66 What is genetic regulation?

Control of gene activation and formation of gene products from transcription to protein formation.

Question 67 Why is gene regulation necessary?

Without it, parts of the cell could overgrow or chemical reactions could overact and kill the cell.

Question 68 What is enzyme regulation?

Control of the activity of already formed enzymes in the cell.

Question 69 What is the function of a promoter?

It controls transcription of DNA into RNA.

Question 70 What is the basal promoter in eukaryotes?

The TATA box and its associated transcription factors.

Question 71 What is the upstream promoter?

A promoter region farther from the transcription start site that contains binding sites for positive or negative transcription factors.

Question 72 What are enhancers?

DNA regions that bind transcription factors and increase transcription.

Question 73 What are insulators?

DNA sequences that block transcriptional influence from surrounding genes.

Question 74 How can DNA methylation affect gene expression?

It can alter insulator function and change whether a gene is expressed.

Question 75 What is one way transcription can be controlled beyond the promoter itself?

By regulatory proteins that act as activators or repressors of transcription.

Question 76 How can the packaging of DNA affect transcription?

Condensed DNA cannot be transcribed, while decondensed DNA can.

Question 77 What is heterochromatin?

Densely packed chromatin in which transcription cannot occur.

Question 78 What is euchromatin?

Loosely packed chromatin that can be transcribed.

Question 79 What are histones?

Positively charged proteins around which DNA is wrapped to form nucleosomes.

Question 80 What is a nucleosome?

The basic repeating unit of chromatin formed by DNA wrapped around histone cores.

Question 81 What is DNA replication?

The process by which DNA makes an exact copy of itself before cell division.

Question 82 When does DNA replication occur in the cell cycle?

Before mitosis, during interphase.

Question 83 Why must DNA replication occur before mitosis?

Because the two daughter cells must each receive a complete copy of the genetic material.

Question 84 What is the first step in cell reproduction?

Replication of all DNA in the chromosomes.

Question 85 What is semiconservative DNA replication?

Each new DNA molecule contains one original strand and one newly synthesized strand.

Question 86 How many strands of each DNA double helix are replicated during DNA replication?

Both strands.

Question 87 In which direction does DNA replication proceed?

In the 5′ to 3′ direction.

Question 88 Which enzyme synthesizes new DNA strands?

DNA polymerase.

Question 89 Which enzyme joins successive DNA nucleotides together?

DNA ligase.

Question 90 What is the replication fork?

The Y-shaped region where DNA strands separate and replication begins.

Question 91 Which enzyme unwinds the DNA double helix before replication?

DNA helicase.

Question 92 What is the role of RNA primase in DNA replication?

It synthesizes short RNA primers to initiate DNA synthesis.

Question 93 What is the function of the RNA primer?

It provides a starting point for DNA polymerase.

Question 94 What is the leading strand?

The DNA strand synthesized continuously toward the replication fork.

Question 95 What is the lagging strand?

The DNA strand synthesized discontinuously away from the replication fork.

Question 96 What are Okazaki fragments?

Short DNA segments synthesized on the lagging strand.

Question 97 What does DNA ligase do with Okazaki fragments?

It joins them into a continuous DNA strand.

Question 98 Why must topoisomerase act during DNA replication?

To prevent overwinding of DNA in front of the replication fork.

Question 99 What is DNA proofreading?

The repair of incorrectly matched nucleotides after DNA replication.

Question 100 Which enzymes are involved in DNA proofreading?

DNA polymerase and DNA ligase.