Chapter 4: Genes and Genetic Diseases Flashcards
What are the basic units of inheritance?
Genes
What are genes composed of?
Sequences of deoxyribonucleic acid (DNA)
What are histones?
A protein constituent of DNA that causes it to coil into a highly compressed structure.
How many genes do humans have?
20,000 to 25,000
What is the genotype?
The composition of genes at a given locus
What is the phenotype?
The outward appearance of an individual, which is the result of both genotype and environment
What are polypeptides?
Intermediate protein compounds, which are in turn composed of sequences of amino acids.
What are amino acids?
organic acids containing NH2
p. 137
(this is ammonia with one of its hydrogen atoms removed; also called amidogen)
The body contains ___ different types of amino acids.
20
What are the subunits of DNA?
nucleotides
Each nucleotide contains:
one pentose sugar (deoxyribose)
one phosphate group
one nitrogenous base (either cytosine, thymine, guanine, or adenine)
How does DNA direct the formation of certain amino acids?
each amino acid is specified by a triplet of nitrogenous bases called codons.
How many possible codons are there? (each codon is a triplet and there are 4 kinds of nitrogenous bases)
4 x 4 x 4 = 64
What is the structure of DNA? (p. 136)
A double helix; envision a twisted ladder with weak hydrogen bonds as the rungs
What enzyme is the most important in the process of DNA replication?
DNA polymerase
What are mutagens? (p. 140)
agents which are known to increase the frequency of mutations (ex: radiation)
Describe the basic steps of DNA replication.
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.
What is the estimated mutation rate in humans?
10 ^ -4 to 10 ^ -7 per gene per generation.
What are 2 primary differences between DNA and RNA?
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)
DNA is formed and replicated in the ____ _______, protein synthesis take place in the _________.
Cell nucleus
Cytoplasm
What fraction of pediatric inpatients are children with genetic diseases?
one-third
