Biochemistry Exam 2 Leys, Bartling, Peters 낱말 카드

Through what two processes do cells acquire nucleotides?

De novo synthesis and salvage pathways

What is the product of de novo purine synthesis?

Inosine

What can the product of de novo purine synthesis, Inosine, be converted into?

Adenosine and guanosine

What regulates de novo purine synthesis at multiple points?

ADP and GDP

Which enzyme recycles hypoxanthine and guanine in the salvage pathway?

Hypoxanthine guanine phosphoribosyl transferase (HGPRT)

What does the enzyme hypoxanthine guanine phosphoribosyl transferase recycle in the salvage pathway?

Hypoxanthine and guanine

What reaction type does xanthine oxidase catalyze?

Hydroxylase

What is formed when xanthine oxidase catalyzes a hydrolase type reaction?

Uric acid that can be excreted

What causes gout?

Excess uric acid

What most often causes gout?

Low levels of uric acid secretion and sometimes excess production

What leads to localized inflammation in joints in gout?

Crystallization of sodium urate in the joints

What deficiency causes Lesch-Nyhan syndrome?

HGPRT

What are the symptoms of Lesch-Nyhan syndrome?

Severe retardation, crippling gouty arthritis, and self mutilation

Why does Lesch-Nyhan syndrome occur only in males?

The HGPRT gene is located on the X chromosome

How can purine breakdown replenish TCA cycle intermediates?

Through the production of fumarate

From what are the atoms in a pyrimidine ring derived?

Aspartate and carbamoyl phosphate

Which pyrimidines can be interconverted?

Uracil (U) and cytosine (C)

What enzyme converts dUMP to TMP?

Thymidylate synthase

What cofactor donates the methyl group in the dUMP to TMP reaction?

Tetrahydrofolate

What are inhibitors of tetrahydrofolate production used to treat?

Cancer and bacterial infections

What do fluorinated pyrimidine analogs inhibit?

Thymidylate synthase

What are fluorinated pyrimidine analogs used for?

Anticancer agents

What does ribonucleotide reductase do?

Converts ribonucleotides to deoxyribonucleotides

What are the base-pairing rules in DNA?

AT and GC

What are the base-pairing rules in RNA?

AU and GC

What can be determined by comparing homologous regions of DNA among species?

Phylogenetic relationships

How do closely related organisms differ in their DNA?

Similar DNA sequences but different chromosomal arrangements

What are the three domains of life?

Bacteria, Archaea, and Eukaryotes

What are the four main processes that generate genomic change?

Intragenic mutation, gene duplication, DNA segment shuffling, horizontal transfer

In a gene comparison among related species, what regions are conserved?

Exons

In a gene comparison among related species, what regions vary in size and content?

Introns

What does most DNA in higher eukaryotes, including humans, not code for?

Proteins

What is most of the human genome made up of?

Repeated sequences

What are many repeated DNA sequences capable of doing?

Moving around in the genome (mobile elements)

What is the shape of bacterial chromosomes?

Circular

What is the shape of eukaryotic chromosomes?

Linear

How can genes be grouped into families?

Based on similar sequences (homologous)

What describes a similar sequence found in different organisms or genes that perform similar functions?

Homologous sequences

What describes when genes have similar functions in very distantly related organisms and can have similar sequences?

Homology

What type of enzyme is DNA polymerase?

DNA dependent DNA synthesizing enzyme

What type of enzyme is RNA polymerase?

DNA dependent RNA synthesizing enzyme

What type of enzyme is reverse transcriptase?

RNA dependent DNA synthesizing enzyme

What type of enzyme is primase?

DNA dependent RNA polymerase

What does primase synthesize?

A short RNA primer

Why does primase synthesize a small RNA primer?

DNA polymerase uses it to elongate the chain

How does DNA polymerase minimize mistakes?

By using a 3' to 5' exonuclease proofreading activity

What is the only direction that DNA polymerase synthesizes DNA?

5' to 3'

To which carbon is each new nucleotide added?

3' of the last nucleotide in the new DNA chain

To which carbon is the base attached on the sugar of a nucleotide?

1'

Between which carbons are adjacent nucleotides linked?

5' and 3'

Which carbon differs between RNA and DNA?

2'

Why does DNA polymerase require a primer for elongation of a new strand?

It cannot initiate synthesis, only elongate existing strands

How many origins of replication do bacterial chromosomes contain?

One

How does DNA synthesis proceed from the origin in bacteria?

In both directions until the two replication forks meet

When can new rounds of DNA replication begin in bacteria?

Before the previous round is completed

How many origins of replication do eukaryotic chromosomes contain?

Many

How often is each eukaryotic chromosome replicated per cell cycle?

Once per division so no new rounds start until after division

What structures are found at the ends of eukaryotic chromosomes?

Telomeres

What enzyme constructs telomeres?

Telomerase

What does telomerase use to synthesize DNA?

An RNA template

Why do polymerase molecules on opposite strands move away from each other?

DNA must be synthesized in the 5' to 3' direction

What enzyme unwinds the DNA strands before replication?

Helicase

What do single-stranded binding proteins do?

Prevent complementary strands from reforming a double helix

Which direction does the leading strand polymerase move?

Toward the replication fork

Which direction does the lagging strand polymerase move?

Away from the replication fork

How is the lagging strand synthesized?

In short Okazaki fragments

What enzyme initiates synthesis of Okazaki fragments?

Primase

How is the leading strand synthesized?

Continuously by DNA polymerase

What happens to DNA to signal that it is unreplicated and ready to be used as a template?

Methylation

What four events generate new or modified genes?

Point mutations, duplication of the entire gene, segment shuffling, and horizontal gene transfer

What describes the mixing of segments of one gene with segments of another gene?

Segment shuffling

What mutation in the coding region changes the amino acid composition of the protein?

Point mutation

What describes the occurrence of two or more distinct forms of a gene or trait in a population?

Polymorphism

What describes the transfer of genes between two organisms that can give new activities?

Horizontal gene transfer

What do genes in a gene family share?

Homologous regions

What do homologous regions shared with genes in a gene family usually code for?

Proteins with similar functions

What facilitates the initiation of recombination?

Breaks in DNA (especially double stranded breaks)

What does a defect in DNA ligase affect?

Joining adjacent DNA

A defect in DNA ligase affects joining of adjacent segments of DNA on a chromosome which can cause what?

Abnormal amounts of recombination

What is the reciprocal exchange of genetic information?

Recombination

Recombination can result from what four causes?

Crossing over, DNA repair, Foreign DNA insertion, Programmed recombination

What is an example of recombination caused by DNA damage?

x-rays

What is an example of programmed recombination during cell development?

Antibody producing genes during B cell maturation

What describes the non-reciprocal exchange of genetic information?

Gene conversion

What happens when recombination occurs between direct repeated sequences on the same chromosome?

Loss of DNA between segments

How can circular DNA insert into a chromosome?

Recombination between a homologous region on circular molecule and chromosome

Where are transposable elements found?

All species from bacteria to humans

What do transposable elements do?

Move from one DNA location to another within the same cell

What can transposable elements cause at the site of insertion?

Changes in DNA

What are the two major types of transposable elements?

Retrotransposons and DNA transposons

What transposable elements have inverted repeats that duplicate a short region at the insertion site?

DNA transposons

What transposable elements are similar to a retrovirus that transposes through an RNA intermediate?

Retrotransposons

What describes recombination caused by imprecise pairing of tandemly repeated sequences?

Unequal crossing-over

What is the result of unequal crossing-over?

Loss or gain of gene copies

What are the two types of mutations?

DNA rearrangements and base substitutions

What do cells have many mechanisms for?

Repairing DNA

What can happen to a damaged nucleotide such as by deamination?

Can be repaired or become a permanent mutation

What are mutations caused by?

Errors during replication or injury from chemicals or radiation

What fraction of the human genome is made of segmental duplications?

About 3%

What describes large regions of DNA present in more than one copy?

Segmental duplications