Molecular Genetics Part II

Flashcard 1

Q: What are the major categories of DNA found in the human genome?

A:

• Exons (~2%)

• Introns (~20%)

• Regulatory sequences (~5%)

• Repetitive DNA (~15%)

• Unique noncoding DNA (~14%)

• Transposable elements (~44%)

Most of the genome does not code for proteins.

Flashcard 2

Q: What percentage of the human genome consists of exons?

A: Approximately 2%.

Exons contain sequences that remain in mature mRNA and often code for proteins.

Flashcard 3

Q: What percentage of the human genome consists of introns?

A: Approximately 20%.

Introns are transcribed into RNA but removed during RNA processing.

Flashcard 4

Q: What percentage of the human genome consists of transposable elements?

A: Approximately 44%.

Transposable elements are the largest component of the human genome.

Flashcard 5

Q: What percentage of the human genome consists of unique noncoding DNA?

A: Approximately 14%.

These sequences do not code for proteins but may have structural or regulatory functions.

Flashcard 6

Q: What percentage of the human genome consists of repetitive DNA?

A: Approximately 15%.

Repetitive DNA consists of sequences repeated many times throughout the genome.

Flashcard 7

Q: What percentage of the human genome consists of regulatory sequences?

A: Approximately 5%.

These sequences regulate gene expression.

Flashcard 8

Q: What is the function of exons?

A: Exons:

• Remain in mature mRNA after splicing.

• Usually contain protein-coding information.

• Are translated into amino acid sequences.

Flashcard 9

Q: What is the function of introns?

A: Introns:

• Are transcribed into pre-mRNA.

• Are removed during RNA splicing.

• Are not translated into protein.

Flashcard 10

Q: Which portions of a gene are removed before translation?

A: Introns are removed during RNA processing.

Flashcard 11

Q: Which portions of a gene remain in mature mRNA?

A: Exons remain in mature mRNA.

Flashcard 12

Q: What are regulatory sequences?

A: DNA sequences that control:

• When genes are expressed

• Where genes are expressed

• How much gene product is produced

Examples include promoters and enhancers.

Flashcard 13

Q: What is repetitive DNA?

A: DNA composed of nucleotide sequences repeated many times within the genome.

Examples:

• Satellite DNA

• Minisatellites

• Microsatellites

Flashcard 14

Q: What is unique noncoding DNA?

A: DNA that:

• Does not code for proteins

• Exists as unique sequences

• May participate in chromosome organization and gene regulation

Transposable Elements Flashcard 15

Q: What are transposable elements?

A: DNA sequences capable of moving from one location in the genome to another.

They are often called "jumping genes."

Flashcard 16

Q: Who discovered transposable elements?

A: Barbara McClintock

Flashcard 17

Q: Why are transposable elements important?

A: They can:

• Create mutations

• Alter gene expression

• Contribute to genome evolution

• Increase genetic diversity

Flashcard 18

Q: What nickname is commonly used for transposable elements?

A: Jumping genes.

Flashcard 19

Q: Which component makes up the largest percentage of the human genome?

A: Transposable elements (~44%).

Alternative Splicing Flashcard 20

Q: What is alternative splicing?

A: A process in which different combinations of exons are joined together from the same pre-mRNA to produce multiple mature mRNAs.

Flashcard 21

Q: Why is alternative splicing important?

A: It allows one gene to produce multiple different proteins.

Flashcard 22

Q: Where does alternative splicing occur?

A: During RNA processing in the nucleus before translation.

Flashcard 23

Q: What molecule undergoes alternative splicing?

A: Pre-mRNA (primary RNA transcript).

Flashcard 24

Q: What is removed during alternative splicing?

A: Introns are removed.

Some exons may also be selectively included or excluded.

Flashcard 25

Q: In alternative splicing, can different mature mRNAs contain different exon combinations?

A: Yes.

Different exon combinations generate different mature mRNAs.

Flashcard 26

Q: A gene contains exons 1, 2, 3, 4, and 5. Give examples of mature mRNAs produced by alternative splicing.

A:
Examples:

• 1-2-3-4-5

• 1-2-4-5

• 1-2-3-5

All can originate from the same gene.

Flashcard 27

Q: Does alternative splicing increase the number of genes in the genome?

A: No.

It increases the number of proteins produced from existing genes.

Flashcard 28

Q: How can a single gene produce several proteins?

A: Through alternative splicing of pre-mRNA.

Flashcard 29

Q: What is the relationship between exons and alternative splicing?

A: Different exons can be included or excluded, creating multiple mature mRNA transcripts.

Flashcard 30

Q: True or False: Every mature mRNA produced from a gene contains all of its exons.

A: False.

Alternative splicing may remove certain exons while retaining others.

Flashcard 31

Q: What is the major biological advantage of alternative splicing?

A: Increased protein diversity without increasing the number of genes.

Flashcard 32

Q: Memorize the approximate composition of the human genome.

A:

• Transposable elements = 44%

• Introns = 20%

• Repetitive DNA = 15%

• Unique noncoding DNA = 14%

• Regulatory sequences = 5%

• Exons = 2%

Key DAT takeaway: Only about 2% of the human genome actually codes for proteins.

Flashcard 33

Q: DAT Rapid Review: Exons vs Introns

A:

Exons	Introns
Remain in mature mRNA	Removed during splicing
Usually translated	Not translated
Protein-coding sequences	Noncoding intervening sequences
~2% of genome	~20% of genome

Flashcard 34

Q: DAT Rapid Review: Alternative Splicing

A:

• Occurs in nucleus

• Acts on pre-mRNA

• Removes introns

• Can include/exclude exons

• Produces multiple mRNAs from one gene

• Increases protein diversity

• Does NOT increase gene number

Classic DAT question: "How can humans make far more proteins than genes?" → Alternative splicing.