Exam #3

double-helical

James Watson and Francis Crick introduced the _____ model for the structure of DNA

deoxyribonucleic acid

full name for DNA

nucleotides

DNA is a polymer of...

nitrogenous base, sugar, phosphate group

Each nucleotide in DNA consists of a ____, a _____, and a ______

Erin Chargaff

reported that the composition of DNA varies between species and that in any species the number of A and T bases are equal and the number of G and C bases are equal

x-ray crystallography

Maurice Wilkins and Rosalind Franklin used a technique called ______ to study molecular structure

purine, pyrimidine

At first, Watson and Crick thought that the bases paired like with like but this did not result in a uniform width. Instead, a _______ is paired with a _____, resulting in a uniform width consistent with the x-ray data

adenine

A

thymine

T

guanine

G

cytosine

C

T

A pairs with...

C

G pairs with...

complementary

the two strands of DNA in a double helix are...

template

Each DNA strand in a double helix acts as a ____ in replication

base-pairing rules

in DNA replication, the parent molecule unwinds, and two new daughter strands are built based on...

dozen

more than a ____ enzymes and other proteins participate in DNA replication

origins of replication

replication begins at particular sites known as _______, where two DNA strands are separated, opening up a replication "bubble"

both

replication proceeds in _____ directions from each origin until the entire molecule is copied

replication fork

at the end of each replication bubble is a _______, a y-shaped region where new DNA strands are elongating

helicases

enzymes that untwist the double helix at the replication forks

single-stranded binding proteins

_______ bind to and stabilize single-stranded DNA

topoisomerase

_______ corrects "overwinding" ahead of replication forks by breaking, swiveling, and rejoining DNA strands

DNA polymerases

_______ cannot initiate synthesis of a polynucleotide; they can only add nucleotides to existing 3' end

3'

DNA polymerases add nucleotides to the ____ end

RNA primer

the initial nucleotide strand in DNA replication is a short....

primase

an enzyme that can start an RNA chain from scratch and adds nucleotides one at a time using the parental DNA as a template

antiparallel

the double helix of DNA is an _____ structure

5' to 3'

a new DNA strand can elongate only in the ______ direction in DNA replication

leading strand

along one template of DNA, the DNA polymerase synthesizes a ______ continuously, moving toward the replication fork

lagging strand

strand of daughter DNA which DNA must work in the direction away from the replication fork; is discontinuous

okazaki fragments

a series of segments that makes up the lagging strand of DNA

DNA ligase

okazaki fragments are joined together by...

DNA replication machine

the proteins that participate in DNA replication form a large complex known as a...

stationary

the DNA replication machine may be _____ during the replication process

mismatch repair

in ______ of DNA, repair enzymes correct errors in base pairing

nucleotide excision repair

in _______ a nuclease cuts out and replaces damaged stretches of DNA

shorter DNA molecules with uneven ends

limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes. There is no way to complete the 5' ends so repeated rounds of replication produce... (not a problem for prokaryotes, most of which have circular chromosomes)

telomeres

eukaryotic DNA molecules have sequences at their ends called... (do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules)

telomerase

an enzyme that catalyzes the lengthening of telomeres in germ cells (if chromosomes in germ cells became shorter every cell cycle, genes would eventually be missing from the gametes)

linear DNA

eukaryotic chromosomes have ______ molecules associated with a large amount of protein

chromatin

DNA is precisely combined with proteins in a complex called...

30-nm fiber

at interphase, some chromatin is organized into a 10-nm fiber, but much is compacted into a ______ through folding and looping

restricted regions

interphase chromosomes occupy specific _______ in the nucleus and the fibers of different chromosomes do not become entangled

mitosis

most chromatin is loosely packed in the nucleus during interphase and condenses prior to...

euchromatin

loosely packed chromatin

heterochromatin

highly condensed chromatin

genetic information

dense packing of heterochromatin makes it difficult for the cells to express _____ coded in these regions

nucleotides

the information content of genes is in the specific sequences of...

proteins

The DNA inherited by an organism leads to instructions for synthesis of...

genotype, phenotype

Proteins are the links between ____ and _____

gene expression

the process by which DNA directs protein synthesis, includes two steps: transcription and translation

RNA

the bridge between genes and the proteins for which they code

Transcription

the synthesis of RNA using information in DNA

messenger RNA (mRNA)

transcription produces...

translation

the synthesis of a polypeptide, using information in the mRNA

Ribosomes

the sites of translation

before

in prokaryotes, translation of mRNA can begin ______ transcription has finished

nuclear envelope

in a eukaryotic cell, the _______ separates transcription from translation

RNA processing

eukaryotic RNA transcripts are modified through __________ to yield the finished mRNA

primary transcript

the initial RNA transcript from any gene prior to processing

central dogma

the concept that cells are governed by a cellular chain of command (DNA---->RNA---->Protein)

20

how many amino acids are there?

4

how many nucleotide bases are there in DNA?

triplet code

the flow of information from gene to protein is based on a ______ (which is a series of nonoverlapping, three-nucleotide words)

mRNA

the three-nucleotide words of a gene are transcribed into complementary nonoverlapping three-nucleotide words of...

polypeptide

mRNA codons are transcribed into a chain of amino acids, forming a...

codons

mRNA base triplets

5' to 3'

During translation, codons are read in the _____ direction

amino acid

each codon specifies the ____ to be placed at the corresponding position along a polypeptide

61

out of 64 triplets, ___ code for amino acids

stop

three triplets are _____ signals to end translation

redundant

the genetic code is ______ (more than one codon may specify a particular amino acid) but not ambiguous (no codon specifies more than one amino acid

reading frame

codons must be read in the correct _______ (correct groupings) in order for the specified polypeptide to be produced

universal

the genetic code is nearly ______, shared by the simplest bacteria to the most complex animals

transplanted

genes can be transcribed and translated after being _______ from one species to another

RNA polymerase

RNA synthesis is catalyzed by ________ which pries the DNA strands apart and adds the RNA nucleotides

complementary

the RNA is ______ to the DNA template strand

primer

RNA polymerase does not need any _____

uracil

RNA synthesis follows the same rules as DNA, except that _____ substitutes for thymine

promoter

the DNA sequence where RNA polymerase attached is called the ________; it is typically 20-35 nucleotides "upstream"

initiation, elongation, and termination

the three stages of transcription are...

untwists

As RNA polymerase moves along the DNA, it _____ the double helix, 10 to 20 bases at a time

40

transcription progresses at a rate of ____ nucleotides per second in eukaryotes

simultaneously

A gene can be transcribed _______ by several RNA polymerases

3'

nucleotides are added to the __ end of the growing RNA molecule

RNA processing

enzymes in the eukaryotic nucleus modify pre-mRNA (___________) before the genetic messages are dispatched to the cytoplasm

both

during RNA processing, _____ ends of the primary transcript are usually altered

spliced

during RNA processing, certain interior sections of the molecule are cut out and the remaining parts are ______ together

5' cap

During RNA processing, the 5' end receives a modified nucleotide _______

poly-A tail

During RNA processing, the 3' end receives a ________

export

the modifications in RNA processing seem to facilitate the ______ of mRNA to the cytoplasm

hydrolytic

the modifications in RNA processing protect mRNA from _______ enzymes

ribosomes

the modifications made in RNA processing helps ______ attach to the 5' end

introns, exons

most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides, called _______, that lie between the coding regions, called ______

RNA splicing

removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence

spliceosomes

sometimes used to carry out RNA splicing, consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites

regulate gene expression

some introns contain sequences that may...

alternative RNA splicing

some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing. This is called...

greater

because of alternative RNA splicing, the number of different proteins an organism can produce is much _____ than its number of genes