Chapter 4: Genes and Genetic Diseases

Question 1

What are the basic units of inheritance?

Answer 1

Genes

Question 2

What are genes composed of?

Answer 2

Sequences of deoxyribonucleic acid (DNA)

Question 3

What are histones?

Answer 3

A protein constituent of DNA that causes it to coil into a highly compressed structure.

Question 4

How many genes do humans have?

Answer 4

20,000 to 25,000

Question 5

What is the genotype?

Answer 5

The composition of genes at a given locus

Question 6

What is the phenotype?

Answer 6

The outward appearance of an individual, which is the result of both genotype and environment

Question 7

What are polypeptides?

Answer 7

Intermediate protein compounds, which are in turn composed of sequences of amino acids.

Question 8

What are amino acids?

Answer 8

organic acids containing NH2

p. 137

(this is ammonia with one of its hydrogen atoms removed; also called amidogen)

Question 9

The body contains ___ different types of amino acids.

Answer 9

20

Question 10

What are the subunits of DNA?

Answer 10

nucleotides

Question 11

Each nucleotide contains:

Answer 11

one pentose sugar (deoxyribose)

one phosphate group

one nitrogenous base (either cytosine, thymine, guanine, or adenine)

Question 12

How does DNA direct the formation of certain amino acids?

Answer 12

each amino acid is specified by a triplet of nitrogenous bases called codons.

Question 13

How many possible codons are there? (each codon is a triplet and there are 4 kinds of nitrogenous bases)

Answer 13

4 x 4 x 4 = 64

Question 14

What is the structure of DNA? (p. 136)

Answer 14

A double helix; envision a twisted ladder with weak hydrogen bonds as the rungs

Question 15

What enzyme is the most important in the process of DNA replication?

Answer 15

DNA polymerase

Question 16

What are mutagens? (p. 140)

Answer 16

agents which are known to increase the frequency of mutations (ex: radiation)

Question 17

Describe the basic steps of DNA replication.

Answer 17

The DNA strand is untwisted and unzipped. A single strand acts as a template.

DNA polymerase pairs the complementary bases; adenine with thymine, and cytosine with guanine.

DNA polymerase adds new nucleotides and “proofreads” the new protein; if not correct, the incorrect nucleotide is excised and replaced.

Question 18

What is the estimated mutation rate in humans?

Answer 18

10 ^ -4 to 10 ^ -7 per gene per generation.

Question 19

What are 2 primary differences between DNA and RNA?

Answer 19

Uracil rather than thymine is present in RNA. (Uracil pairs with adenine.) Also, RNA usually occurs as a single strand rather than a double like DNA. (p. 141)

Question 20

DNA is formed and replicated in the ____ _______, protein synthesis take place in the _________.

Answer 20

Cell nucleus

Cytoplasm

Question 21

What fraction of pediatric inpatients are children with genetic diseases?

Answer 21

one-third