USABO Open Exam Questions and Answers
(2026 Edition) | Solved Exam Pack | 100%
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• Euchromatin -✓✓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 -✓✓This shows as dark areas on the eukaryotic
nucleas; it is densly packed chormatin (DNA and protein complex)
which cannot be transcribed.
• Histones -✓✓Special proteins around which DNA is wrapped.
• Lamins -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓Cell organelle responsible for
synthesizing proteins.
• Catalytic site -✓✓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 -✓✓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 -✓✓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 -✓✓The constant release of small amounts of a
substances from the cell membrane.
• Regulated release -✓✓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 -✓✓The process by which substances are exported from a
cell.
• Phagocytosis/Endocytosis -✓✓The process by which substances or
pathogens are taken in to a cell by engulfment by a vesicular structure
surrounded by cell membrane.
• Lysosomes -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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,
(2026 Edition) | Solved Exam Pack | 100%
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• Euchromatin -✓✓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 -✓✓This shows as dark areas on the eukaryotic
nucleas; it is densly packed chormatin (DNA and protein complex)
which cannot be transcribed.
• Histones -✓✓Special proteins around which DNA is wrapped.
• Lamins -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓Cell organelle responsible for
synthesizing proteins.
• Catalytic site -✓✓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 -✓✓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 -✓✓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 -✓✓The constant release of small amounts of a
substances from the cell membrane.
• Regulated release -✓✓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 -✓✓The process by which substances are exported from a
cell.
• Phagocytosis/Endocytosis -✓✓The process by which substances or
pathogens are taken in to a cell by engulfment by a vesicular structure
surrounded by cell membrane.
• Lysosomes -✓✓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 -✓✓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 -✓✓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 -✓✓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 -✓✓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,
