USABO Exam Questions and
Complete Solutions Graded A+
Eukaryote - Answer: An organism whose cells contain complex structures enclosed within membranes.
The defining membrane bound structure thats sets them apart from prokaryotic cells is the nucleas or
nuclear envelope within which the genetic material is carried. All species of large complex species are
eukaryotes, including animals, plants and funghi.
Euchromatin - Answer: This shows as pale areas in the nucleas under electro magnification. It is a less
densly packed form of chromatin; 10% is even less condensed and in this form it can be actively
transcribed to produce RNA.
Heterochromatin - Answer: This shows as dark areas on the eukaryotic nucleas; it is densly packed
chormatin (DNA and protein complex) which cannot be transcribed.
Histones - Answer: Special proteins around which DNA is wrapped.
Lamins - Answer: Intermediate filament proteins which protect the structure of the nucleas, they
polymerize to from a network of filaments that lie just within the nuclear membrane. The network of
these filament proteins is called the nuclear lamina.
Nuclear Lamina - Answer: The network of intermediate nuclear filament proteins (Lamins) which is
located just below the nuclear membrane and is linked to the membrane and chromatin.
Nuclear Pores - Answer: 9nm (approx) gaps in the nuclear envelope that allow the passage of RNA and
ribosomes out of the nucleas and the entry of selected small proteins and small water soluble
molecules.
Prokarayotes - Answer: An organism of the kingdom of Monera, comprising the bacteria and
cyanobacteria. Characterised by the abscence of a distinct, membrane bound nucleas or membrane
bound organelles and by DNA that is not organised in to chromosomes. Also called moneran.
,Protoctist - Answer: Any of various unicellular eukaryotic organisms and their multicellular, coenocytic
or colocial descendants that belong to the kingdom of Protocista according to some taxonomic systems.
The protoctists include protozoans, slime moulds, various algae and other groups. In many new
classification systems, all proctists are considered protists.
Signal Sequence - Answer: Affectionately known as the 'address label' of a polypeptide. A short (3-60
amino acids long) peptide chain that directs the transport of a protein. These may also be called
targeting signals, signal peptides, transit peptides, or localization signals.
The amino acid sequences of these direct proteins (which are synthesized in the cytosol) to certain
organelles such as the nucleus, mitochondrial matrix, endoplasmic reticulum, chloroplast, apoplast and
peroxisome. Some signal peptides are cleaved from the protein by signal peptidase after the proteins
are transported.
Endoplasmic Reticulum - Answer: The endoplasmic reticulum (ER) is a eukaryotic organelle that forms an
interconnected network of tubules, vesicles, and cisternae within cells. Rough endoplasmic reticula
synthesize proteins, while smooth endoplasmic reticula synthesize lipids and steroids, metabolize
carbohydrates and steroids (but not lipids), and regulate calcium concentration, drug metabolism, and
attachment of receptors on cell membrane proteins. Sarcoplasmic reticula solely regulate calcium levels.
Smooth endoplasmic reticulum - Answer: Cell organelle responsible for attachment of receptors on cell
membrane proteins, synthesizing lipids and steroids, metabolizing carbohydrates and steroids (but not
lipids) and regulating calcium concentration and drug metabolism.
Rough endoplasmic reticulum - Answer: Cell organelle responsible for synthesizing proteins.
Catalytic site - Answer: In molecular biology this site is part of an enzyme where substrates bind and
undergo a chemical reaction.The majority of enzymes are proteins but RNA enzymes called ribozymes
also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid
residues (or nucleotides in ribozymes) that participate in recognition of the substrate. Residues that
directly participate in the catalytic reaction mechanism are called active site residues.
Vesicles - Answer: Small lipid-bounded spheres which transport proteins, glyco proteins and newly
synthesized lipids (which are imbedded in the sphere itself) from the endoplasmic reticulum to the Golgi
Apparatus or from the Golgi apparatus to another destination. They move short distances by the process
of difussion, moving long distances requires the assistance of proteins associated with microtubules.
,Golgi apparatus - Answer: This is an organelle found in all eukaryotic cells.It was identified in 1897 by the
Italian physician Camillo Golgi, after whom it is named. It processes and packages proteins after their
synthesis and before they make their way to their destination; it is particularly important in the
processing of proteins for secretion. Its size varies in different types of cells depending on cell function; a
hormone secreting cell will contain a far larger version of this organelle than a muscle cell for example. It
also forms a part of the cellular endomembrane system.
Constitutive release - Answer: The constant release of small amounts of a substances from the cell
membrane.
Regulated release - Answer: The release of substances from a cell membrane only when specific
conditions exist. A good example is the release of gastrointestinal hormones and digestive enzymes in
response to food.
Exocytosis - Answer: The process by which substances are exported from a cell.
Phagocytosis/Endocytosis - Answer: The process by which substances or pathogens are taken in to a cell
by engulfment by a vesicular structure surrounded by cell membrane.
Lysosomes - Answer: Small organelles which contain digestive enzymes with an internal pH of around 5.
They are responsible for breaking down large molecules taken in to the cell by phagocytosis and also for
the breaking down of old organelles.
Peroxisomes - Answer: Organelles that are plentiful in liver cells and adipocytes, responsible for breaking
down fatty acids and amino acids in to hydrogen peroxide (among other things) via the action of an
enzyme known as catalayse.
MItochondrian - Answer: Sausage shaped organelles with a double membrane. The inner membrane
folds in to cristae. This organelle plays a fundamental role in the production of ATP in eukarayote cells
and they are abundant in cells which require high amounts of energy such as muscle cells.
Cristae - Answer: Internal compartments formed by the inner membrane of a mitochondrion. They are
studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for
, chemical reactions to occur is within the mitochondria. This allows cellular respiration (aerobic
respiration since the mitochondrion requires oxygen) to occur.
Mitochondrial DNA - Answer: The DNA located in mitochondria
It can be regarded as the smallest chromosome, and was the first significant part of the human genome
to be sequenced. In most species, including humans, mtDNA is inherited solely from the mother. The
DNA sequence of mtDNA has been determined from a large number of organisms and individuals
(including some organisms that are extinct), and the comparison of those DNA sequences represents a
mainstay of phylogenetics, in that it allows biologists to elucidate the evolutionary relationships among
species. It also permits an examination of the relatedness of populations, and so has become important
in anthropology and field biology.
Mitochondrial Matrix - Answer: This matrix contains soluble enzymes that catalyze the oxidation of
pyruvate and other small organic molecules.
It also contains the mitochondria's DNA and ribosomes. The word "matrix" stems from the fact that this
space is viscous, compared to the relatively aqueous cytoplasm.
Cell Wall - Answer: An extracellular structure in plants which is rigid and surrounds the cell membrane
giving it shape and support, like playtex for plants lol! It is primarily composed of cellulose which is a
polysaccharide.
Plastids - Answer: These are major organelles found in the cells of plants and algae. They are the site of
manufacture and storage of important chemical compounds used by the cell, often containing pigments
used in photosynthesis. The types of pigments present can change or determine the cell's color.These
organelles are responsible for photosynthesis, storage of products like starch and for synthesis. All types
are derived from proplastids (formerly "eoplasts", eo-: dawn, early), which are present in the
meristematic regions of the plant. Proplastids and young chloroplasts commonly divide, but more
mature chloroplasts also have this capacity.
Chloroplasts - Answer: These plant organelles have their own DNA like mitochondria. They are normally
larger than mitochondria though and they also have a three membrane system.
Thylakoid - Answer: A thylakoid is a membrane-bound compartment inside chloroplasts and
cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist
of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks
of disks referred to as grana (singular: granum). Grana are connected by intergrana or stroma thylakoids,
which join granum stacks together as a single functional compartment.
Complete Solutions Graded A+
Eukaryote - Answer: An organism whose cells contain complex structures enclosed within membranes.
The defining membrane bound structure thats sets them apart from prokaryotic cells is the nucleas or
nuclear envelope within which the genetic material is carried. All species of large complex species are
eukaryotes, including animals, plants and funghi.
Euchromatin - Answer: This shows as pale areas in the nucleas under electro magnification. It is a less
densly packed form of chromatin; 10% is even less condensed and in this form it can be actively
transcribed to produce RNA.
Heterochromatin - Answer: This shows as dark areas on the eukaryotic nucleas; it is densly packed
chormatin (DNA and protein complex) which cannot be transcribed.
Histones - Answer: Special proteins around which DNA is wrapped.
Lamins - Answer: Intermediate filament proteins which protect the structure of the nucleas, they
polymerize to from a network of filaments that lie just within the nuclear membrane. The network of
these filament proteins is called the nuclear lamina.
Nuclear Lamina - Answer: The network of intermediate nuclear filament proteins (Lamins) which is
located just below the nuclear membrane and is linked to the membrane and chromatin.
Nuclear Pores - Answer: 9nm (approx) gaps in the nuclear envelope that allow the passage of RNA and
ribosomes out of the nucleas and the entry of selected small proteins and small water soluble
molecules.
Prokarayotes - Answer: An organism of the kingdom of Monera, comprising the bacteria and
cyanobacteria. Characterised by the abscence of a distinct, membrane bound nucleas or membrane
bound organelles and by DNA that is not organised in to chromosomes. Also called moneran.
,Protoctist - Answer: Any of various unicellular eukaryotic organisms and their multicellular, coenocytic
or colocial descendants that belong to the kingdom of Protocista according to some taxonomic systems.
The protoctists include protozoans, slime moulds, various algae and other groups. In many new
classification systems, all proctists are considered protists.
Signal Sequence - Answer: Affectionately known as the 'address label' of a polypeptide. A short (3-60
amino acids long) peptide chain that directs the transport of a protein. These may also be called
targeting signals, signal peptides, transit peptides, or localization signals.
The amino acid sequences of these direct proteins (which are synthesized in the cytosol) to certain
organelles such as the nucleus, mitochondrial matrix, endoplasmic reticulum, chloroplast, apoplast and
peroxisome. Some signal peptides are cleaved from the protein by signal peptidase after the proteins
are transported.
Endoplasmic Reticulum - Answer: The endoplasmic reticulum (ER) is a eukaryotic organelle that forms an
interconnected network of tubules, vesicles, and cisternae within cells. Rough endoplasmic reticula
synthesize proteins, while smooth endoplasmic reticula synthesize lipids and steroids, metabolize
carbohydrates and steroids (but not lipids), and regulate calcium concentration, drug metabolism, and
attachment of receptors on cell membrane proteins. Sarcoplasmic reticula solely regulate calcium levels.
Smooth endoplasmic reticulum - Answer: Cell organelle responsible for attachment of receptors on cell
membrane proteins, synthesizing lipids and steroids, metabolizing carbohydrates and steroids (but not
lipids) and regulating calcium concentration and drug metabolism.
Rough endoplasmic reticulum - Answer: Cell organelle responsible for synthesizing proteins.
Catalytic site - Answer: In molecular biology this site is part of an enzyme where substrates bind and
undergo a chemical reaction.The majority of enzymes are proteins but RNA enzymes called ribozymes
also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid
residues (or nucleotides in ribozymes) that participate in recognition of the substrate. Residues that
directly participate in the catalytic reaction mechanism are called active site residues.
Vesicles - Answer: Small lipid-bounded spheres which transport proteins, glyco proteins and newly
synthesized lipids (which are imbedded in the sphere itself) from the endoplasmic reticulum to the Golgi
Apparatus or from the Golgi apparatus to another destination. They move short distances by the process
of difussion, moving long distances requires the assistance of proteins associated with microtubules.
,Golgi apparatus - Answer: This is an organelle found in all eukaryotic cells.It was identified in 1897 by the
Italian physician Camillo Golgi, after whom it is named. It processes and packages proteins after their
synthesis and before they make their way to their destination; it is particularly important in the
processing of proteins for secretion. Its size varies in different types of cells depending on cell function; a
hormone secreting cell will contain a far larger version of this organelle than a muscle cell for example. It
also forms a part of the cellular endomembrane system.
Constitutive release - Answer: The constant release of small amounts of a substances from the cell
membrane.
Regulated release - Answer: The release of substances from a cell membrane only when specific
conditions exist. A good example is the release of gastrointestinal hormones and digestive enzymes in
response to food.
Exocytosis - Answer: The process by which substances are exported from a cell.
Phagocytosis/Endocytosis - Answer: The process by which substances or pathogens are taken in to a cell
by engulfment by a vesicular structure surrounded by cell membrane.
Lysosomes - Answer: Small organelles which contain digestive enzymes with an internal pH of around 5.
They are responsible for breaking down large molecules taken in to the cell by phagocytosis and also for
the breaking down of old organelles.
Peroxisomes - Answer: Organelles that are plentiful in liver cells and adipocytes, responsible for breaking
down fatty acids and amino acids in to hydrogen peroxide (among other things) via the action of an
enzyme known as catalayse.
MItochondrian - Answer: Sausage shaped organelles with a double membrane. The inner membrane
folds in to cristae. This organelle plays a fundamental role in the production of ATP in eukarayote cells
and they are abundant in cells which require high amounts of energy such as muscle cells.
Cristae - Answer: Internal compartments formed by the inner membrane of a mitochondrion. They are
studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for
, chemical reactions to occur is within the mitochondria. This allows cellular respiration (aerobic
respiration since the mitochondrion requires oxygen) to occur.
Mitochondrial DNA - Answer: The DNA located in mitochondria
It can be regarded as the smallest chromosome, and was the first significant part of the human genome
to be sequenced. In most species, including humans, mtDNA is inherited solely from the mother. The
DNA sequence of mtDNA has been determined from a large number of organisms and individuals
(including some organisms that are extinct), and the comparison of those DNA sequences represents a
mainstay of phylogenetics, in that it allows biologists to elucidate the evolutionary relationships among
species. It also permits an examination of the relatedness of populations, and so has become important
in anthropology and field biology.
Mitochondrial Matrix - Answer: This matrix contains soluble enzymes that catalyze the oxidation of
pyruvate and other small organic molecules.
It also contains the mitochondria's DNA and ribosomes. The word "matrix" stems from the fact that this
space is viscous, compared to the relatively aqueous cytoplasm.
Cell Wall - Answer: An extracellular structure in plants which is rigid and surrounds the cell membrane
giving it shape and support, like playtex for plants lol! It is primarily composed of cellulose which is a
polysaccharide.
Plastids - Answer: These are major organelles found in the cells of plants and algae. They are the site of
manufacture and storage of important chemical compounds used by the cell, often containing pigments
used in photosynthesis. The types of pigments present can change or determine the cell's color.These
organelles are responsible for photosynthesis, storage of products like starch and for synthesis. All types
are derived from proplastids (formerly "eoplasts", eo-: dawn, early), which are present in the
meristematic regions of the plant. Proplastids and young chloroplasts commonly divide, but more
mature chloroplasts also have this capacity.
Chloroplasts - Answer: These plant organelles have their own DNA like mitochondria. They are normally
larger than mitochondria though and they also have a three membrane system.
Thylakoid - Answer: A thylakoid is a membrane-bound compartment inside chloroplasts and
cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist
of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks
of disks referred to as grana (singular: granum). Grana are connected by intergrana or stroma thylakoids,
which join granum stacks together as a single functional compartment.
