The Human Genome

Question 1

What is genetics?

Answer 1

Genetics is the scientific study of heredity, which involves the process of how traits and characteristics are passed from parents to offspring.

Question 2

What is a gene?

Answer 2

A gene is a unit of biological information that carries the instructions for the synthesis of a specific protein or regulatory molecule. Genes are segments of DNA located on chromosomes.

Question 3

What is precision medicine?

Answer 3

Precision medicine is an emerging approach to disease treatment and prevention that takes into account individual variability in genes, environment, and lifestyle for each person. It utilizes data-driven methods to tailor medical decisions and interventions to optimize outcomes for individuals.

Question 4

What are the key components considered in precision medicine?

Answer 4

Precision medicine considers the individual’s genetic makeup, environmental factors, and lifestyle choices to develop personalized treatment and prevention strategies. It aims to provide more targeted and effective healthcare based on specific characteristics of each patient.

Question 5

How are sugars connected in nucleotides?

Answer 5

Sugars in nucleotides are connected via phosphate groups through a bond called a phosphodiester bond.

Question 6

Where does the phosphodiester bond occur in the sugar-phosphate backbone?

Answer 6

The phosphodiester bond forms between the 3’ carbon atom of one sugar molecule and the 5’ carbon atom of the next sugar molecule in the sugar-phosphate backbone of DNA or RNA.

Question 7

What is the significance of new nucleotides being added to the 3’ -OH end?

Answer 7

During DNA or RNA synthesis, new nucleotides are added to the 3’ carbon atom of the growing chain. This occurs because the 3’ carbon has a hydroxyl (OH) group that can react with the phosphate group of the incoming nucleotide, forming the phosphodiester bond and extending the chain.

Question 8

How is the double helix structure of DNA composed?

Answer 8

The double helix structure of DNA is composed of two strands that run in opposite directions, known as antiparallel strands. The strands are held together by hydrogen bonds between complementary base pairs.

Question 9

What is the uniform diameter of the DNA double helix?

Answer 9

The DNA double helix has a uniform diameter throughout its structure.

Question 10

How do the opposite bases on each strand of DNA complement each other?

Answer 10

In DNA, adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). These opposite bases on each strand form complementary base pairs held together by hydrogen bonds.

Question 11

What are the major and minor grooves in the DNA double helix?

Answer 11

The DNA double helix has two grooves running along its length, known as the major groove and the minor groove. These grooves are formed by the arrangement of the bases and provide sites for protein binding and interactions. The major groove is wider and more accessible than the minor groove, allowing proteins to interact with the exposed edges of the bases.

Question 12

What is the basic chemistry of DNA replication?

Answer 12

During DNA replication, nucleotides are added to the 3’ end of the growing DNA strand. This occurs because DNA polymerases can only add nucleotides to the 3’ carbon of the existing DNA chain.

Question 13

Why does replicating both strands of DNA present an issue?

Answer 13

The antiparallel nature of the DNA double helix creates an issue during replication. While one strand, called the leading strand, can be continuously synthesized in the 5’ to 3’ direction, the other strand, called the lagging strand, is synthesized in short fragments known as Okazaki fragments. This is because DNA replication occurs in a continuous manner only in the 5’ to 3’ direction.

Question 14

How are the lagging strand fragments joined together?

Answer 14

The Okazaki fragments on the lagging strand are eventually joined together by DNA ligase, creating a continuous complementary strand.

Question 15

What is the significance of nucleotides being added to the 3’ end during DNA replication?

Answer 15

The addition of nucleotides to the 3’ end of the growing DNA strand ensures that the DNA chain extends in the correct direction, following the 5’ to 3’ polarity of the original DNA template.

Question 16

What is the molecular biology of DNA replication?

Answer 16

DNA replication involves the synthesis of two new DNA strands, known as the leading strand and the lagging strand. The antiparallel nature of DNA requires different mechanisms for their replication.

Question 17

How is the leading strand synthesized during DNA replication?

Answer 17

The leading strand is synthesized continuously in the same direction as the replication fork moves. DNA polymerase adds nucleotides in a 5’ to 3’ direction, following the template strand in the 3’ to 5’ direction. This results in the leading strand being synthesized continuously.

Question 18

How is the lagging strand synthesized during DNA replication?

Answer 18

The lagging strand is synthesized discontinuously in the opposite direction of the replication fork movement. Due to the antiparallel nature of DNA, DNA polymerase cannot directly synthesize the lagging strand in one continuous process. Instead, it synthesizes short fragments called Okazaki fragments in the 5’ to 3’ direction away from the replication fork.

Question 19

How are the Okazaki fragments on the lagging strand connected to form a continuous strand?

Answer 19

After the synthesis of Okazaki fragments, DNA ligase joins them together, sealing the gaps and forming a continuous complementary lagging strand.

Question 20

Why does the lagging strand require discontinuous replication?

Answer 20

Discontinuous replication of the lagging strand is necessary because DNA synthesis occurs only in the 5’ to 3’ direction, while the lagging strand template runs in the 3’ to 5’ direction.

Question 21

What is happening during DNA replication based on the provided diagram?

Answer 21

Based on the diagram, the process of DNA replication is depicted. The double-stranded DNA molecule is unwinding and opening, creating two separated strands.

Question 22

What is the leading strand in DNA replication?

Answer 22

The leading strand is one of the DNA strands being replicated during DNA replication. It is synthesized continuously in the 5’ to 3’ direction as DNA polymerase adds nucleotides along the template strand.

Question 23

What is the lagging strand in DNA replication?

Answer 23

The lagging strand is the other DNA strand being replicated during DNA replication. It is synthesized discontinuously in short fragments called Okazaki fragments. Primers are required for each Okazaki fragment, and DNA synthesis occurs in the 5’ to 3’ direction away from the replication fork.

Question 24

Why does the lagging strand require further primer binding and exhibit discontinuous DNA synthesis?

Answer 24

The lagging strand is synthesized discontinuously because DNA polymerase can only add nucleotides in the 5’ to 3’ direction. As the replication fork moves, new primers are required to initiate DNA synthesis on each Okazaki fragment, resulting in discontinuous synthesis.

Question 25

How is chromatin structured?

Answer 25

Chromatin, which consists of DNA and associated proteins, is mostly compact. Euchromatin is compacted approximately 1000-fold, while heterochromatin and metaphase chromosomes are compacted about 10,000-fold.

Question 26

What is the fundamental subunit of chromatin?

Answer 26

The fundamental subunit of chromatin is the nucleosome. It is composed of eight histone proteins around which approximately 146 base pairs of DNA are wrapped.

Question 27

How do nucleosomes arrange in chromatin?

Answer 27

Nucleosomes form a “bead-on-a-string” configuration, where the DNA is wrapped around the histone proteins, resembling beads on a string.

Question 28

How are nucleosomes further organized in chromatin?

Answer 28

Nucleosomes are further coiled and folded into fibers and loops, contributing to the higher-order organization of chromatin. These structures help compact the DNA and regulate access to the genetic information stored within it.

Question 29

How is DNA organized in the cell?

Answer 29

DNA is organized into chromosomes, which are structures composed of DNA tightly packed and associated with proteins.

Question 30

When are chromosomes visible?

Answer 30

Chromosomes are only visible at certain stages of the cell cycle, particularly during cell division. They become highly condensed and observable under a microscope during metaphase, when they align at the center of the cell.

Question 31

What is the significance of chromosomes in the cell cycle?

Answer 31

Chromosomes play a crucial role in cell division, as they contain the genetic information necessary for the replication and inheritance of traits. They ensure the proper distribution of DNA to daughter cells during mitosis and meiosis.

Question 32

What are the main stages of the cell cycle?

Answer 32

The main stages of the cell cycle are mitosis and cytokinesis, which are followed by interphase. Interphase consists of G1 (Gap 1), S (DNA synthesis), and G2 (Gap 2) phases.

Question 33

What happens during G1 phase of the cell cycle?

Answer 33

G1 phase is a resting stage where cells prepare for DNA replication and cell division. Non-dividing cells may arrest at this stage, known as the G0 phase, where they remain in a quiescent state.

Question 34

What occurs during the S phase of the cell cycle?

Answer 34

The S phase is the DNA synthesis phase, during which DNA replication takes place. The genetic material is duplicated, resulting in two identical copies of each chromosome.

Question 35

What happens during G2 phase of the cell cycle?

Answer 35

G2 phase is a period of preparation for mitosis. Cells undergo further growth and prepare for cell division by synthesizing necessary proteins and organelles.

Question 36

What are cell cycle checkpoints?

Answer 36

Cell cycle checkpoints are control mechanisms that monitor the integrity of DNA and ensure proper progression of the cell cycle. They regulate cell cycle progression and prevent the division of damaged or genetically unstable cells.

Question 37

How are cell cycle checkpoints controlled?

Answer 37

Cell cycle checkpoints are controlled by cyclins, which are proteins that regulate the activity of protein kinases. Cyclins and protein kinases work together to ensure proper cell cycle progression and respond to signals such as DNA damage or incomplete replication.

Question 38

What is mitosis?

Answer 38

Mitosis is a process of cell division in which one parent nucleus gives rise to two daughter nuclei. The daughter nuclei are genetically identical to each other and to the parent nucleus.

Question 39

What are the main events of mitosis?

Answer 39

Prophase: Chromosomes condense, the nuclear envelope breaks down, and spindle fibers begin to form.
Metaphase: Chromosomes align at the equatorial plane (metaphase plate) of the cell.
Anaphase: Sister chromatids separate and move to opposite poles of the cell.
Telophase: Chromosomes decondense, nuclear envelopes reform around the separated sets of chromosomes, and cytokinesis begins.

Question 40

What is the size and composition of the mitochondrial genome?

Answer 40

The mitochondrial genome is approximately 16.6 thousand base pairs (kbp) in size. It lacks repetitive sequences, with only 87 base pairs being intergenic (located in the D-loop). It contains 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes, and 13 protein-coding genes.

Question 41

What is the size and composition of the nuclear genome?

Answer 41

The nuclear genome is much larger, with approximately 3.2 billion base pairs (3,200,000,000 or 3.2 x 10^9 bp). It consists of a majority of high-copy-number repetitive elements. It is estimated to contain around 20,000 genes, which produce approximately 100,000 proteins.