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USABO Exam Questions and Answers
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USABO Exam Questions and Answers
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USABO Exam Questions and AnswersEukaryote - 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.
Stroma - Answer -Stroma (fluid), the fluid in between grana, where carbohydrate
formation reactions occur in the chloroplasts of plant cells photosynthesizing
Glycosaminoglycans (GAG's) - Answer -Also known as mucopolysaccharides these are
long unbranched polysaccharides consisting of a repeating disaccharide unit. The
repeating unit consists of a hexose (six-carbon sugar) or a hexuronic acid, linked to a
hexosamine (six-carbon sugar containing nitrogen). These are the major component of
the 'gel' found in the extracellular matrix of tissue. They are negatively charged and thus
attract ions, especially sodium which aids diffusion of water in to the tissue, giving tissue
it's compression resistance.
Extracellular Matrix - Answer -This matrix is secreted by cells and laid down externally
and it's properties vary enormously depending on it's chemical composition and which
tissue is being examined. In some cells it acts as cement or scaffolding. In plants it can
be associated with individual cells.
Elastin - Answer -An flexible protein found in the extra cellular matrix of blood vessels.
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