USABO Exam Questions and Answers
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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.
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.
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.
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.
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.
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
