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267 Cards in this Set

  • Front
  • Back
Eukaryotic cells sequester most of their DNA in the ___.
nucleus
The nucleus occupies about ___% of cell volume.
10
T/F: Nuclei may be spherical, elongated, flattened or lobed depending on the cell type.
true
Nuclei are usually located in the ___ of cells, although there are exceptions.
center
T/F: All cells at some point have a nucleus.
true
An example of a cell without a central nucleus
fat cell
the five main structures of the nucleus
nuclear envelope
chromatin
nuclear matrix
nucleoli
nucleoplasm
the fluid substance in which the solutes of the nucleus are dissolved
nucleoplasm
T/F: Nucleoplasm is analogous to cytoplasm.
false
The ___ is a protein-containing fibrillar network, the insoluble material left in the nucleus after a series of biochemical extraction steps.
nuclear matrix
The nuclear matrix is thought to act as a ___.
scaffold
The constituent proteins of the nuclear matrix may bind ___, which could serve several functions.
chromosomes
functions of the constituent proteins of the nuclear matrix binding chromosomes
1. help organize chromosomes (localize genes)
2. help regulate gene expression
3. help regulate DNA replication
The ___ separates the eukaryotic cell's genetic material from the cytoplasm.
nuclear envelope
The nuclear envelope serves as a ___ regulating ___ of materials.
barrier
entry and exit
The nuclear envelope consists of the ___ and ___ membranes.
inner
outer
The inner and outer membranes of the nuclear envelope are about ___ nm apart.
10-50
The inner and outer membranes of the nuclear envelope are fused together at regularly interspersed circular passageways known as ___.
nuclear pores
The space between the two membranes of the nuclear envelope is known as the ___.
perinuclear space
The inner and outer nuclear membranes are ___ but have different ___.
continuous
functions
The inner and outer nuclear membranes maintain distinct ___ compositions.
protein
The inner nuclear membrane contains proteins specialized to bind the ___.
nuclear lamina
a thin meshwork of intermediate filament proteins covering the inside surface of the inner membrane
nuclear lamina
Three functions of the nuclear lamina:
1. provides ___ for the inner membrane
2. a site of attachment for ___
3. has a presumed role in ___
1. mechanical support
2. chromatin
3. DNA transcription and translation
The filaments of the nuclear lamina are composed of proteins called ___.
lamins
___ mutations are responsible for various human diseases such as Hutchinson-Guilford progeria syndrome.
lamin gene
a disease caused by lamin gene mutations which causes premature aging and death during teen years
Hutchinson-Guilford progeria syndrome
The outer nuclear membrane is continuous with the membrane of the __.
ER
The ___ is continuous with the ER lumen.
perinuclear space
The outer membrane is studded with ___.
ribosomes
The outermembrane of the nuclear envelope is supported by a loosely organized network of ___.
intermediate filaments
The average mammalian cell nucleus is peppered with several thousand ___.
nuclear pores
Associated with each nuclear pore is a ___.
nuclear pore complex (NPC)
The nuclear pore complex is a hub of activity with a large volume of ___ traffic.
bi-directional
The ___ is a basket-like apparatus consisting of about ___ different proteins (___).
nuclear pore complex (NPC)
30-50
nucleoporins
The ___ fills the nuclear pore like a stopper.
nuclear pore complex (NPC)
The basket portion of the NPC "hangs" into the ___.
nucleus
NPCs move material across the ___ in both directions.
nuclear membrane
___ molecules may freely diffuse through the aqueous pores in the NPC.
small water-soluble
Larger molecules move through the NPC via ___.
active transport
NPCs provide a relatively large channel through which molecules can pass without ___.
restructuring
T/F: Proteins may pass fully folded through the NPC.
true
___ subunits may pass fully assembled through NPCs.
ribosomal
For the import of molecules through the nuclear pores into the nucleus, nuclear proteins must bear a ___ (NLS).
nuclear localization signal
The NLS-protein binds ___, and the resulting complex associates with a cytoplasmic filament.
importins
Steps in the import of molecules into the cell nucleus
1. Nuclear proteins bearing a nuclear localization signal (NLS) binds importins
2. The resulting complex associates with a cytoplasmic filament
3. The filament guides the complex through the pore
4. NLS-protein is released on the nuclear side
5. Importins are transported back to the cytoplasm (energy of GTP is required)
Proteins exported from the nucleus contain ___ (NES).
nuclear export signals
Most cytoplasm-bound molecules are ___.
mRNAs
A protein complex binds newly synthesized mRNAs to guide them through the ___ into the ___.
NPC
cytoplasm
the basic building block of DNA
nucleotide
a dense-staining region of the nucleus; a large aggregate of macromolecules needed for the assembly of ribosomes
nucleolus
The nucleolus is a large aggregate of macromolecules needed for the assembly of ___.
ribosomes
T/F: The nucleolus does not have a membrane.
true
the main components of the nucleolus
proteins
rRNAs (ribosomal RNA)
rRNA genes (located on certain chromosomes)
T/F: Nucleoli are capable of fusion.
true
The nucleolus disassociates at the beginning of ___ and then reforms at its conclusion.
mitosis
five unifying characteristics of life
organization
metabolism
reproduction
development
cellular composition (all living things are made up of cells)
"All living things are made up of cells"
cellular composition
There are over ___ cell types in the human body.
200
All cells arise from ___ cells. This is true of both unicellular and multicellular organisms.
preexisting
In multicellular organisms, the ___ gives rise to all other cells that make up the organism.
egg cell
The egg contains ___ that is being faithfully passed along to all other cells.
hereditary information
Without exception, all living things on earth store hereditary information in long chemical polymers known as ___.
deoxyribonucleic acids (DNA)
All information regarding an organism is stored in just ___ strung together in long linear sequences (DNA).
four monomers
the four monomers in which all information regarding an organism is stored
the nucleotides A, C, G, and T
T/F: The four nucleotides are quite sufficient to store the complexity of an entire genome.
true
The ___ is the basic monomeric building block of DNA (and RNA).
nucleotide
the three basic parts of a nucleotide
a sugar (pentose)
a nitrogenous base
a phosphate group
the two types of sugars (monosaccharides) found in nucleotides
riboses (RNA)
deoxyriboses (DNA)
the two types of bses in DNA
purines
pyrimidines
1. ___ consist of two rings.
2. ___ consist of one ring.
1. purines
2. pyrimidines
the two purines
guanine
adenine
the three pyrimidines
cytosine
thymine
uracil
T/F: Nucleotides are polarized molecules.
true
the two distinct ends of nucleotides
5'
3'
The 5' end of a nucleotide is the location of the ___ group; the 3' end is the location of the ___ group.
phosphate
sugar
Stacked nucleotides form a single DNA strand and give the molecule ___.
polarity
Adjacent (stacked) nucleotides are bound from ___ to ___.
phosphate
sugar
The adjacent (stacked) nucleotides are bound from phosphate to sugar (deoxyribose), creating a sugar-phosphate ___.
backbone
Nucleotide ___ project from the backbone.
bases
In 1953, ___ and ___ proposed a structural model for DNA - the double helix.
Watson
Crick
In 1953, Watson and Crick proposed a structural model for DNA - the ___.
double helix
The Watson-Crick Model:
1. The DNA molecule is composed of ___.
2. The strands ___ around each other.
3. The strands are ___ and ___.
4. The sugar-phosphate backbones are on the ___ of the molecule.
5. The bases project ___.
6. The two strands are held together by ___ between opposite bases.
1. two strands of nucleotides
2. spiral
3. antiparallel, complementary
4. outside
5. inward
6. hydrogen bonds
Nucleotides:
C's and ___ go together; A's and ___ go together.
G's
T's
A-T have ___ H bonds (2); C-G have ___ H bonds (3).
weaker
stronger
___ are the principal building blocks of all organisms.
proteins
T/F: Proteins can only function in a certain configuration.
true
Protein configuration is determined by ___. This sequence is determined by ___.
amino acid sequence
nucleotide sequence in DNA
___ contains an organism's genetic information, encoded in the linear organization of nucleotides.
DNA
An organism's genetic information is contained in the linear organization of the ___ of the DNA.
nucleotides
An organism's genetic information must be transmitted to the protein synthesizing machinery - the ___ allows for RNA transcription.
double helix
the segment of DNA (series of base pairs) corresponding to a single protein or RNA
gene
a distinct unit of inheritance which determines the characteristics of species and individuals
gene
a body (structure) in the cell nucleus that contains genes
chromosome
Chromosomes are composed of ___ and associated ___.
DNA
proteins
Word root of chromosome:
chromo = ___
some = ___
colored
body
The stereotypical representation of a chromosome is really only visible during ___ of the cell cycle.
mitosis (metaphase, or mitotic, chromosome)
T/F: For a significant part of the cell cycle, nuclear DNA does not take the form of chromosomes.
true
For a significant part of the cell cycle, nuclear DNA has a ___ appearance and is composed of ___.
puffed, stringy
chromatin
In preparation for cell division, nuclear DNA must be ___.
replicated
Following replication, DNA must organize itself in a manner allowing it to be evenly distributed to two new ___, i.e., chromatin organizes itself into ___.
daughter cells
chromosomes
A chromosome as we see it during mitosis is really a ___.
pair of chromosomes
pair of chromosomes = ___
homologous chromosomes
There are normally ___ chromosomes in human somatic cells (___ from each parent).
46
23
Since we have two of each chromosome (homologous chromosomes), we also have two of each ___ on the chromosome.
gene
Since we have two of each chromosome, we also have two of each gene on the chromosome; corresponding genes are likely to be ___.
different
Each copy of a gene is referred to as an ___.
allele
the part of the chromosome where a gene is located
locus
different forms of a gene at a gene locus, often denoted by letters such as A or a
alleles
The presence of two copies of the same gene allows for ___ of one allele over another.
dominance
The presence of two copies of the same gene allows for dominance of one allele (___ gene) over another (___ gene).
dominant
recessive
If a trait is recessive (e.g., albinism), an individual must carry two ___ (one from each parent) in order for the trait to manifest itself.
recessive alleles
The ___ is all the DNA - coding and non-coding - occurring in one haploid (23 chromosomes) set of chromosomes in one individual.
genome
The ___ represents the collective body of information present in a species.
genome
In humans, the genome consists of ___ base pairs.
about 3.1 billion
The average DNA molecule (chromosome) is ___ long and ___ thick.
2 inches
2nm
Keeping the proportion of DNA's length and thickness, an 8-inch thick telephone pole would rise ___ above the earth.
2500 miles
___ total meters of DNA must be correctly packaged into every nucleated cell.
2
A nucleus ___ in diameter must pack in DNA ___ times this length.
10 micrometers
200,000
T/F: Chromosomes can seemingly appear out of nowhere and suddenly disappear.
true
The organization of DNA within chromosomes exists on a spectrum from ___ to incredibly ___.
diffuse
compact
In a ___ cell, chromosomes are fairly diffuse (chromatin).
non-mitotic
In a ___ cell, chromosomes are very compact (sister chromatids)
mitotic
___ represent the lowest level of chromosomal organization.
nucleosomes
A ___ is a unit consisting of DNA wrapped multiple times around a complex of histone proteins.
nucleosome
A nucleosome is a unit consisting of DNA wrapped multiple times around a complex of ___ proteins.
histone
Nucleosomes are joined together like ___ to form chromatin.
beads on a string
Nucleosomes are joined together like beads on a string to form ___.
chromatin
The next level of chromatin organization after being formed from nucleosomes features organized packaging into ___.
30nm fibers
Nucleosomes in a 30 nm fiber are thought to be packaged in two ways: ___ and ___
zig-zag
solenoid
Nucleosomes organize to ___; next to ___; then to ___; then to ___; then to ___.
chromatin
30nm fibers
loops
300nm fiber
sister chromatids
A further level of chromatin organization features irregular ___ of 30nm fibers; these are then tethered to proteins forming a scaffold and then they coil to form a ___.
loops
fiber about 300nm in diameter
The 300nm looped chromatin fibers perform a final coil to form ___. This final coil shortens the DNA ___fold.
sister chromatids (700 nm diameter)
10
The ___ chromosome represents the ultimate in chromatin organization and compactness.
metaphase
1 micrometer of metaphase chromosome contains ___ of DNA (packing ration of ___).
1 cm
10,000:1
A gene is said to be expressed when its genetic information is transferred to ___ and then to ___.
mRNA
protein
DNA to mRNA = ___
transcription
transcription = ___ to ___
DNA
mRNA
mRNA to protein = ___
translation
translation = ___ to ___
mRNA
protein
The flow of genetic information from DNA to RNA to protein is common to all cells - this flow is termed the ___.
central dogma of molecular biology
the same information transferred from one format to another
transcription
Our genetic information is stored in the cell ___ as ___.
nucleus
DNA
the two ways our genetic information stored as DNA in the cell nucleus is used
1. it must be passed along to daughter cells (DNA replication)
2. it must be copied in order to make proteins for use in the current cell (RNA synthesis, i.e, transcription)
the two basic constraints the cell must overcome in obtaining protein from DNA; the solution to these problems is ___
1. segregation of cellular activities
2. size of DNA molecules
transcription
Chromosomal DNA resides in the ___; the synthesis of proteins takes place in the ___.
nucleus
cytoplasm
(so info from DNA must be transferred to the cytoplasm)
Chromosomal DNA totals ___ base pairs (the entire genome).
3.2 billion
T/F: If the cell needs to synthesize a specific protein, only information from a few thousand base pairs may be required.
true
In transcription, the cell needs a method of extracting the ___ from a long strand of DNA.
short segment of information required
___ is the intermediate between a gene and its protein.
mRNA
___ is a small, mobile nucleic acid which carries information from the nucleus to the cytoplasm.
mRNA
RNA is similar to DNA in that both molecules are composed of ___.
nucleotides
Major differences between DNA and RNA molecules:
1. DNA is composed of the sugar ___; RNA's sugar is ___.
2. DNA contains ___, RNA contains ___ to pair up with adenine.
3. DNA forms a double-___; RNA forms ___.
1. deoxyribose
ribose
2. thymine
uracil
3. helix
varied structures
RNA is composed of the sugar ___.
ribose
DNA is composed of the sugar ___.
deoxyribose
DNA serves as a ___ from which mRNA is assembled (transcription).
template
mRNA assembly
transcription
The mRNA transcript migrates from the nucleus to a ___ where translation occurs (protein assembly).
ribosome
protein assembly = ___
translation
Polymerases are ___.
enzymes
Transcription is catalyzed by enzymes known as ___.
RNA polymerases
RNA polymerases produce a single-strand RNA that is ___ to one strand of DNA.
complementary
RNA polymerase binds to a region of DNA called the ___.
promoter
In transcription, attachment of the ___ causes the DNA to unwind and the two strands to separate.
RNA polymerase
In transcription, after attachment of the RNA polymerase causes the DNA to unwind and the two strands to separate, complementary ___ bind to one strand of DNA.
RNA nucleotides
In transcription, after attachment of the RNA polymerase causes the DNA to unwind and the two strands to separate and complementary RNA nucleotides bind to one strand of DNA, the RNA polymerase then assembles the nucleotidews into a(n) ___.
mRNA chain
T/F: RNA polymerases operate somewhat differently in prokaryotic cells vs. eukaryotic cells.
true
T/F: The details of eukaryotic transcription are simpler and were elucidated first.
false (prokaryotic is simpler)
In both prokaryotes and eukaryotes, RNA polymerases much search for a ___ region on the DNA.
promoter
The promoter region of a gene indicates a ___ for transcription of an mRNA.
start site
The promoter region of a gene indicates a start site for ___.
transcription of an mRN
Promoter regions are highly ___. In eukaryotes this is known as the ___ for the heavy presence of thymines and adenines.
conserved (present across species)
TATA
Prokaryotic RNA polymerases form loose associations with the DNA and require the help of an accessory polypeptide, called the ___, to find the correct start site for transcription.
sigma factor
T/F: Sigma factor separates from the RNA polymerase following the initiation of transcription.
true
Eukaryotic RNA polymerases cannot initiate transcription without a series of ___.
protein factors
the series of protein factors required for eukaryotic RNA polymerases to initiate transcription (to correctly position the RNA polymerase at the promoter)
general transcription factors
T/F: In both eukaryotes and prokaryotes, RNA polymerase will cause unwinding of the DNA helix and separation of the strands
true
In transcription in both eukaryotes and prokaryotes, ___ nucleotides of the DNA are separated at a time.
20
In transcription in both eukaryotes and prokaryotes, 20 nucleotides of the DNA are separated at a time - called the ___.
transcription bubble
the one strand of DNA that serves as a template from which an RNA molecule will be synthesized
template strand
RNA polymerase must locate a gene's ___ in order to initiate transcription.
promoter
T/F: A gene contains only one promoter
true
The strand containing the promoter serves as the ___ strand.
template
T/F: In theory two mRNA's could be obtained from a DNA molecule.
true
RNA is transcribed from the template strand of ___, and a ___ RNA strand is synthesized.
DNA
complementary
When RNA is transcribed from the template strand of DNA, the actual information contained in the RNA is ___ to the other (non-template) strand.
identical
When RNA is transcribed from the template strand of DNA, the actual information contained in the RNA is identical to the ___ strand.
other (non-template) strand
The non-template strand is sometimes referred to as ___ and the template strand as ___.
sense
antisense
RNA polymerases move along the DNA strand in a ___ , direction.
3' to 5'
RNA is synthesized in a ___ direction.
5' to 3'
In RNA synthesis, nucleotide triphosphates are added at the ___ end.
3'
Elongation occurs at about ___ nucleotides/sec.
50
T/F: RNA polymerase can move in either direction relative to the double-stranded DNA molecule.
true
T/F: RNA polymerase can only move in one direction relative to the template strand.
true
RNA polymerase can move in either direction relative to the ___ molecule, but it can only move in one direction relative to the ___ (3' to 5' direction).
double-stranded DNA molecule
template strand
T/F: In both eukaryotes and prokaryotes, the configuration of DNA can present obstacles to the RNA polymerase (chromatin structure, DNA supercoiling).
true
T/F: Because of obstacles to the RNA polymerase, the movement of RNA polymerase is usually not smooth.
true
2 obstacles to the RNA polymerase found in the configuration of DNA
chromatin structure
DNA supercoiling
Both prokaryotic and eukaryotic RNA polymerases require ___ to navigate DNA during transcription.
proteins
___ prevent RNA polymerases from detaching prematurely.
elongation factors
___ and ___ reduce DNA supercoiling.
DNA gyrases
topoisomerases
In both prokaryotes and eukaryotes, the signal for termination is encoded in the ___.
gene (a specific DNA sequence)
In prokaryotes, termination is essentially a ___ event that follows elongation.
single step
In eukaryotes, termination occurs in conjunction with an ___ that prepare the mRNA for translation.
intricate series of processing steps
In prokaryotes, RNA polymerase looks for a consensus sequence in the gene, called the ___, that tells it to stop.
terminator
In prokaryotes when the RNA polymerase finds the terminator, the polymerase stops and releases both the ___ and the ___.
DNA template
new mRNA
After termination, the RNA polymerase searches for a new ___ so that transcription may start again.
sigma factor
The terminator is thought to code for an ___ structure.
RNA hairpin
The RNA hairpin structure coded for by the terminator "derails" the RNA polymerase releasing ___, ___ and ___.
DNA
RNA
polymerase
The terminator is an ___ rich sequence.
A-T
The DNA-RNA hybrid of the terminator is formed mainly by ___ base pairs (two hydrogen bonds are easier to break).
A-U
Transcription in prokaryotes is a relatively straightforward process that occurs in three basic stages: ___, ___ and ___.
initiation
elongation
termination
The net result of transcription is a transcript ___ that is an unprocessed copy of DNA, ready to be translated.
mRNA
In eukaryotes, the processing of mRNA for final use by the cell occurs ___ transcription, elongation and termination.
during and after
Transcription involves making a copy of all nucleotides between the ___ and the ___.
promoter
terminator
T/F: In eukaryotes not all of the transcribed mRNA molecule (pre-mRNA) will code for a protein.
true
Important parts of the pre-mRNA are the ___ which function in the regulation of translation.
untranslated regions
the two important structures that must be part of the final mRNA to be exported from the nucleus
1. 7-methyl guanosine cap
2. poly-A tail
___ and ___ ensure the mRNA will be properly exported from the nucleus and interact with a ribosome for translation.
a 7-methyl guanosine cap
a poly-A tail
A 7-methyl guanosine cap and a poly-A tail ensure that the mRNA will be properly exported from the nucleus and interact with a ___ for translation.
ribosome
The pre-mRNA is organized into two basic regions: ___ and ___.
introns
exons
___ do not code for the protein and are removed from the pre-mRNA in translation.
introns
These segments of pre-mRNA code for a protein and are eventually spliced together.
exons
the purpose of introns
allow one gene to code for several different proteins
We have about ___ different genes but about ___ different mRNAs.
25,000
100,000
the three basic levels at which gene expression is regulated
transcriptional (DNA)
processing (RNA)
translational (protein)
mechanisms determining whether and how often a gene is transcribed = ___-level control
transcriptional
nature of mRNA obtained from transcript = ___-level control
processing
mechanisms determining whether and how often an mRNA is translated = ___-level control
translational
An ___ is a simple copy of the DNA from which it was transcribed.
mRNA
Nucleotides are copied as ___.
nucleotides
T/F: Converting mRNA into protein is more complex than transcribing mRNA.
true
In translation, the language of ___ must be translated into the language of ___.
nucleotides
amino acids
Proteins are essentially a string of ___.
amino acids
The order of the amino acids in proteins is determined by the order of ___.
nucleotides in the gene (DNA)
the order of nucleotides in the gene = the ___
mRNA
The code for the protein is contained in the sequences of ___.
nucleotides
T/F: In translation, the order of nucleotides in the gene (the mRNA) must be read and translated.
true
mRNA molecules are read in sets of ___.
three
each set of three nucleotides = a ___
codon
Each codon codes for a particular ___.
amino acid
T/F: Most amino acids have more than one codon.
true
Most amino acids have more than one ___.
codon
The protein synthesizing machinery must read the mRNA codons, and a ___ determines where reading starts.
start codon
A "start" codon determines where reading the mRNA codons starts, and this sets the ___.
reading frame
___ are adaptor molecules responsible for matching amino acids to mRNA codons.
transfer RNAs (tRNAs)
T/F: Amino acids do not directly recognize a codon, so a tRNA is needed.
true
There are many tRNA genes, about ___ of which are known.
48
tRNAs form a cloverleaf about ___ in length.
80 nucleotides
the two important regions in the tRNA
the anticodon
the amino acid binding site
The ___ region of the tRNA binds the mRNA codon.
anticodon
The ___ region of the tRNA carries the appropriate amino acid.
amino acid binding site
tRNAs bind ___ from the intercellular pool, which requires the energy of ___.
amino acids
ATP
After binding amino acids from the intracellular pool, the tRNAs then take the amino acids to the ___ for incorporation into the growing peptide chain.
ribosome
There are ___ known codons, but only ___ anticodons (tRNAs).
61
48
Since there are 61 known codons and only 48 anticodons, some anticodons must be able to bind to codons that are not an ___.
exact match
T/F: The first twonucleotides of a codon require a stringent base pairing, while the third nucleotide of a codon permits a mismatch.
true
The ___ nucleotides of a codon require a stringent base pairing.
first two
The ___ nucleotide of a codon permits a mismatch.
third
The third nucleotide of a codon permits a mismatch - this is known as ___.
wobble base pairing
___ base pairing allows a codon to base pair with more than one anticodon.
wobble
___ are the site of translation
ribosomes
nucleotide to amino acid = ___
translation
Ribosomes are ___ for the synthesis of protein.
catalysts
A typical eukaryotic cell may contain ___ ribosomes.
one million
Ribosomes consist of two molecules: ___ and ___.
proteins (over 50 different types)
rRNA
The proteins and rRNA of ribosomes are assembled into ___.
two subunits