Honors Biology Midterm Review Worksheet KEY
I.
What are the seven characteristics of life?
 Composed of cells
 Reproduce
 Require energy and raw material
 Maintain homeostasis (the ability to maintain constant internal conditions [e.g.,
temperature, salt levels, pH] no matter how the outside environment changes.)
 Respond to stimuli
 Grow and/or repair damage
 Can evolve
II.
Make the following conversions:
40 mm  m
40 mm 
III.
3 cg  μg
27 mL  1 000 000 μL = 27 000 μL
1 000 mL
3 cg  1 000 000 μg = 30 000 μg
100 cg
Complete the following table, using a periodic table of the elements:
Element
Carbon
Sodium
Curium
IV.
27 mL  μL
1m
= .04 m
1 000 mm
Symbol
C
Na
Cm
Protons
6
11
96
Neutrons
6
12
151
Electrons
6
11
96
The ions of elements are very important in biology. Define valence electrons and ion.
Give the charge and magnitude of the ions formed by fluorine and sodium.
Electrons are arranged in shells that orbit the nucleus. Elements try to either gain,
lose, or share enough electrons to have eight in their outer shell (octet rule). These
outermost electrons are called valance electrons, and are involved in bonding. Ions
are atoms that have either gained or lost electrons to fulfill the octet rule. (As an
aside, some elements have four electrons in their valance shell. These are most likely
to form covalent bonds, because it is too difficult to either gain or lose four electrons.)
Sodium has 11 electrons, 2 in shell 1, 8 in shell 2, and 1 in the outer valence shell: it
will give this outer shell electron to any atom that will take it, so that the filled shell
right below it becomes the outer valence shell. Sodium ions have a charge of +1 (11
protons, 10 electrons). Fluorine has 9 electrons, 2 in shell 1, 7 in shell 2; it must
acquire an addition electron to fill its valence shell so the ion has a charge of -1 (9
protons, 10 electrons).
What is an isotope?
Isotopes are atoms with the same number of protons (thus they are the same element),
but different numbers of neutrons. Therefore, they have different weights. Isotopes
are often radioactive.
V.
Water is a polar molecule. Explain a polar covalent bond, and then describe the
special attributes of water because it is polar that make it important to biology.
Polar covalent bonds form within molecules. It is the unfair sharing of electrons
within a covalent bond, and in biology often forms between oxygen and hydrogen.
The result of a polar bond is a dipole, a molecule with δ+ (slight positive) δ- ends.
Hydrogen bonds form between two or more polar molecules (like water), when a
δ+ end is electrostatically attracted to a δ- end (opposites attract).
Because of hydrogen bonds, water is highly cohesive (sticks together), leading to
capillary action, surface tension, the ability to dissolve other polar molecules and
ionic compounds, and to expand when frozen.
Define hydrophobic and hydrophilic; give an example substance for each.
Hydrophilic (water loving) molecules dissolve well in water (e.g., sugar, salt,
alcohol). Hydrophobic (water fearing) molecules cannot dissolve in water (e.g., oil,
fats).
VI.
Describe pH. Define an acid and a base. Give an example of each
For this elementary level, pH is the concentration (amount) of H+ ions (or protonsthey are the same thing) in a solution. An acid has a high concentration of H+ ions,
and has a pH less than 7 (e.g., hydrochloric acid, citric acid). A base has a very low
concentration of H+ ions and has a pH greater than 7 (e.g., soap, drain cleaner). Pure
water is neutral, with a pH of 7.
VII.
Sketch the following organic functional groups: amino, carboxylic acid, methyl,
alcohol, phosphate.
VIII.
Complete the table below:
Type of
Biomolecule
Name of
monomer
Name(s) of
polymer
Nucleic Acid
Nucleotide
DNA or RNA
Proteins
Amino acid
Protein or
Polypeptide
Lipids
Fatty acid
Triglyceride
Carbohydrate
Monosaccharide or
simple sugar
Starch, cellulose,
glycogen, chitin
IX.
Role in the cell
or biology
Information storage,
ribozymes
Enzymes
Structural components,
Messengers
Energy storage,
membranes
Energy storage
Structural components
H
N
O
O
NH
N
C
Phospholipid
Starch, glycogen
Chitin, Cellulose
O-
HO
C
H
H
N
O
CH
CH
CH
OH
CH
OH
OH
Carbohydrate
H
OH
CH
HC
OH
CH2
O
H
CH2
C
H
NH2
HO
O
H
N
N
P
mRNA,
chromosomes
Ligase, Helicase
Keratin
Insulin
Identify the following biomolecules:
O
-O
Example(s)
H
HC
NH
Nucleic acid
Amino Acid
O
H2
C
H3C
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
C
C
H2
OH
Saturated Fatty acid
X.
Describe dehydration synthesis and hydrolysis, including how they work and what
they do.
Dehydration synthesis creates polymers (long chains of smaller monomers). An
enzyme holds two monomers adjacent to each other in its active site, so that an -OH
group from one monomer and an -H from the other react to form water (HOH, or
H2O). The monomers left behind then reform the broken bond by linking to each
other, which forms a polymer
Hydrolysis is the opposite—it breaks down polymers into monomers. An enzyme
binds the polymer in its active site, and holds it so that a water molecule can float in
and attack a bond. The water splits into H and OH, one going to each of the two new
pieces the polymer was broken into.
XI.
Shape is one of the most important aspects of a biological molecule. The structure of
a protein can be described at four levels. Briefly describe each.
Primary (1°) structure- the order of amino acids encoded in the DNA
Secondary (2°) structure- special shapes the amino acids fold into, such as α-helixes
and β-pleated sheets.
Tertiary (3°) structure- the overall 3-D shape of the protein
Quaternary (4°) structure- not in all proteins; when multiple proteins work together to
accomplish their job
XII.
Heat and pH changes can denature a protein. What does this mean?
Heat and pH denature or change the shape of a protein. This is especially dangerous
for enzymes: if the active site changes shape, the enzyme can no longer function.
Changes in salt concentration and certain toxins also denature proteins.
XIII.
What is an enzyme? Draw a standard reaction curve, and show the effect an enzyme
has on the curve.
An enzyme is a protein that catalyzes (speeds up) a chemical
reaction by lowering the activation energy (EA). It is not
consumed in the reaction, and can function repeatedly. In this
diagram, the uncatalyzed reaction is in blue, and the enzyme
catalyzed reaction in red.
XIV. Describe how an enzyme catalyses a reaction.
Substrates fit into a groove on the enzyme called the active site—the shape of the
active site is specific enough so that only one substrate or type of substrate can fit
inside. Once in the active site, the enzyme holds the substrate in the correct position
so that bonds can be broken or made easily. When done, the products diffuse out of
the active site, and fresh reactants can diffuse in.
XV.
What are two ways to regulate (control) an enzyme?
Competitive inhibition occurs when a plug-like regulator molecule competes with the
substrate to enter and then block the active site. If there is a lot of substrate around,
the competition is fierce and it takes along time for the regulators to shut down all the
enzymes.
Noncompetitive inhibition is similar, but the regulator has its own site to bind to (thus
no competition with the substrate). When bound, this molecule often changes the
shape of the active site so that substrates no longer fit.
XVI. Differentiate between prokaryotic and eukaryotic cells.
Prokaryotes have no nucleus or membrane bound organelles (examples are the
bacteria and archaea). Eukaryotes have nuclei.
XVII. Describe the role of the following organelles: cell membrane, nucleus, nucleolus,
rough ER, smooth ER, Golgi apparatus, lysosomes, peroxisomes, mitochondria,
chloroplasts, centrioles, cytoskeleton, cell wall, large central vacuole
 Cell membrane- selectively permeable barrier made of phospholipids and proteins
(both integral and peripheral), along with cholesterol and carbohydrates
 Nucleus- double-membrane sack that contains the DNA in eukaryotes; continuous
with the ER, and studded with nuclear pores
 Nucleolus- dark mass within the nucleus, site where rRNA and ribosomal proteins
are transcribed (it is not a true structure, but an artifact of microscopy; but it is
still testable)
 Rough ER- tubes of membrane studded with ribosomes (large molecule masses
that build proteins from mRNA); site of protein synthesis for exported or
membrane proteins
 Smooth ER- same as rough ER, but without the ribosomes. Sites of exported and
membrane protein transport (and some modification)
 Golgi bodies- put final modifications on proteins destined for the membrane or
export; package them into vesicles
 Lysosomes- sacks containing digestive enzymes
 Peroxisomes- sacks containing highly reactive peroxides—involved in defense
and apoptosis (along with lysosomes)
 Mitochondria- double-membrane bound organelles; the inner membrane is folded
into cristæ. Site of Krebs cycle and the electron transport chain; source of most of
the ATP used by the cell. Once believed to be a free living bacterium according
to the endosymbiotic theory. Has its own DNA and ribosomes, and reproduces by
binary fission.
 Chloroplasts- very similar to mitochondria, a double membrane structure with
internal thylakoid sacks stacked into grana. Site of light reactions and Calvin
cycle of photosynthesis. Also believed to one have been a free-living bacterium
 Centrioles- only in animal cells; anchors aster microtubules during mitosis and
meiosis
 Cytoskeleton- made of actin fibers and microtubules, give cell shape and support
 Cell wall- cellulose cage in plant cells (and some fungi—but made of chitin)
serves as osmotic shock absorber and serves as plant skeleton
 Large central vacuole- found only in plant cells, it is filled with water so that the
cells are constantly pushing against the cell wall. This serves as the plant
skeleton.
XVIII. In general terms, describe the pathway an exported protein would follow from start to
finish. Compare this to a cytosolic protein. (For this question, you can omit the
actual molecular steps in transcription and translation, and only focus on the
organelles.)
Exported/Membrane Protein: mRNA exits the nucleus through a nuclear pore and
binds to a ribosome on the rough ER. The ribosome translates the protein, which then
moves into the rough ER, then travels to the smooth ER, and finally is pinched off
into a vesicle and dragged to the Golgi body. The Golgi body modifies the protein as
needed, and then packs them into a vesicle, which moves to cell membrane and fuses,
pushing out the contents.
Cytosolic Protein: the mRNA exits the nucleus through nuclear pores and binds a
cytosolic ribosome, which translates the protein. The protein remains in the cytosol.
XIX. If you said that the cell membrane is made of recycled Golgi body, you would be
correct. Explain.
All the membranes in a cell are interchangeable—as vesicles pinch off the smooth
ER, they fuse and become part of the Golgi; as vesicles pinch off the Golgi, they fuse
and become one with the cell membrane. Phago- and pinocytic vesicles from the cell
membrane fuse with the ER and Golgi to replenish their membranes.
XX.
The cell membrane is composed of phospholipids. Describe them.
Phospholipids are composed of two hydrophobic fatty acids and a hydrophilic
phosphate head, making it an amphipathic molecule. The membrane itself is made of
two layers of phospholipids, arranged so that the hydrophobic tails are buried together
on the inside and the hydrophilic heads are exposed to the water.
XXI. What can pass through the cell membrane without help? What cannot? What are the
two ways you can get something across the membrane that normally cannot cross it?
Can: small molecules (water, O2, CO2) and hydrophobics (lipids—especially steroids)
Cannot: large molecules (sugars, proteins), ions (Na+, F-), and hydrophilic molecules.
Active transport moves substances that cannot cross by using energy (ATP)—this is
also a good way to move against a concentration gradient. Facilitated diffusion
simply provides a transport tube so that substances can go in and out of the cell—but
they still must obey the rules of diffusion.
XXII. Define hypotonic, isotonic, and hypertonic. Describe what would happen to a cell
placed in each. Why are plant cells more resistant to osmotic shock than other cells?
A Hypotonic solution contains less dissolved substances than what you are comparing
it to; isotonic solutions have the same, and a hypertonic solution has more dissolved
substances. Water will move from hypotonic to hypertonic solutions. Cells placed in
a hypotonic solution will have water rush into it, causing the cell to swell and
eventually burst. Cells placed in isotonic solutions have no change. Cells places in
hypertonic solutions will lose water and shrink (crenellate if red blood cells). Plant
cells do not rupture in hypotonic solutions due to the protection of their cell wall.
XXIII. Glucose is the preferred source of energy for your cells. Describe what happens to it
during cellular respiration.
Glucose is split into two pyruvates (aka pyruvic acids) in glycolysis. As the
pyruvates are transported across the mitochondrial double membranes, one carbon
leaves as CO2, the other two form acetyl-CoA. In the Krebs cycle, the two carbons in
acetyl-CoA are eventually lost as two CO2 as well.
XXIV. You get most of your energy from the electron transport chain. Describe how it
works. Make sure you give the source of the electrons, what happens as they travel,
and where they end up.
Electrons are brought to the ETC by NADHH+ or FADH2. They pass through three
proton pumps, which use their energy to move two protons each (6 total from
NADHH+ and 4 total from FADH2) from the inside of the mitochondria to the intermembrane space. At the end of the ETC, the electrons are picked up by O2, which is
converted into H2O. Next to the ETC is the F1F0 ATP Synthase. Because of the
pumping, protons become highly concentrated in the intermembrane space. They
flow along their concentration gradient back into the cell through the ATP synthase.
As they flow through the ATP synthase, they cause parts to spin like a water wheel.
Every two protons give the ATPase enough energy to covert ADP + Pi  ATP.
Plants get most of their energy from the electron transport chain. Describe how the
ETC in chloroplasts work, making sure to mention where the electrons come from,
what happens as they travel, and where they end up.
Sunlight strikes a magnesium atom held in a plant pigment like chlorophyll held near
on photosystem II (PSII), knocking two electrons out of magnesium’s valence shell.
The electrons then pass through one proton pump, which pumps two protons from
outside the thylakoid to inside the thylakoid membrane. Meanwhile, the electrons
continue through photosystem I (PSI) which uses light to reenergize the moving
electrons. At the end of the chain, the electrons are picked up by NADP+, which
carries the electrons to the Calvin cycle or other places they are needed. In order to
restore the electrons lost by magnesium in chlorophyll, photosystem II (PSII) takes
two electrons from a water molecule, which decays into 2 H+ and eventually O2.
XXV. A swimmer is competing in the 500 yard freestyle.
In order to be the most
hydrodynamic (and thus move the fastest), he must have his face in the water for most
of the race. His strenuous muscle activity demands huge amount of oxygen, and he
rapidly uses up all of the O2 in his blood stream. Even with a shortage of oxygen, the
swimmer can not only complete the 500 yard course but win the race. How? Why do
his muscles ache the next day? What would be different if he were yeast?
The swimmer will rapidly begin fermentation in his muscle cells. Only glycolysis
will occur, giving him 2 ATP per glucose. Glycolysis requires large amounts of
NAD+—in order to regenerate it, the body dumps the electrons in NADHH+ into
pyruvate, which is converted into lactic acid. The acid burns caused by lactic acid are
what make his muscles sore. If he was a yeast cell, the swimmer would produce
ethanol (alcohol), which would quickly kill him by dehydrating his muscle cells.
XXVI. Draw the four stage of mitosis. Label the important parts.
A diagram has handed out in class; you can also download it from the website. Make
sure you drawing shows:
 Prophase: nuclear membrane disappears; chromosomes condense and become
visible, centrioles move to opposite poles of the cell, spindle fibers (asters) form
 Metaphase: chromosomes are pushed/pulled into the middle of the cell


Anaphase: the centromeres are cut, and the chromosomes are pulled to the
opposite sides of the cell
Telophase: asters disappear, nuclei reform, chromosomes decondense and
disappear
XXVII.
Give the four phases of the cell cycle. What are checkpoints?
Mitosis  G1 (growth phase 1 or Gap 1)  Synthesis  G2
 G0 (cell does not divide)
Checkpoints occur between the different stages. Cells will only move onto the
next stage if (1) they have to (e.g., to repair damage) and (2) the earlier stage was
completed correctly
Pyrimidine Base
XXVIII.
Describe the structure of DNA. Label 3’ and 5’.
DNA is made of nucleotides, which are composed of a 5carbon deoxyribose sugar, a phosphate group, and a
nitrogenous base. There are four bases: the purines (2
rings) adenine and guanine and the pyrimidines (1 ring)
cytosine and thymine. DNA is an antiparallel double
helix, with the sugar and phosphates on the outside and
the bases on the inside. The bases are held together by
hydrogen bonds (3 between G-C, 2 between A-T). The
two strands run antiparallel (opposite) one another.
NH2
N
Phosphate Group
N
O
5'
-O
P
O
O-
CH2
C H
H
O
H C
C
C
OH
H
H
3'
Deoxyribose
Give the complimentary strand for this DNA: 5’-AGGCTTAGGCTT-3’
3’-TCCGAATCCGAA-5’
XXIX. Describe how DNA is replicated, giving the role of all five enzymes. Draw a
replication fork, and show the leading and lagging strand.
Helicase unzips the double helix,
which is then held apart by SSB.
Primase puts down a short RNA
primer, and then DNA Polymerase builds a new strand of
DNA, reading the original strand
3’  5’. The lagging strand is
built in short Okazaki fragments;
these are linked together by
Ligase.
XXX. What is transcription? How does RNA polymerase know where to start? How does
it know where to stop?
Transcription is the copying of DNA into RNA. RNA polymerase binds to a
promoter and then copies the DNA into RNA. It stops when it hits a terminator.
O
XXXI. What are the four types of RNA that can be produced through transcription?
mRNA encodes proteins. rRNA make up ribosomes. tRNA is involved in transports
amino acids and recognizes codons in translation. Ribozymes are RNA enzymes
(like the snRPs in the spliceosome and some rRNAs)
XXXII.
What are the three modifications done to mRNA, and why are they done?
The mRNA gets a methyl-guanine cap (mG cap) for protection, a poly(A) tail to
serve as a timer, and is spliced so that interrupting introns are removed from the
coding exons.
XXXIII.
Describe how a ribosome and tRNA make protein.
A ribosome binds to the mRNA, and aligns it so that the start codon, AUG, is in
the middle P slot. The tRNA that reads this codon, and carries the amino acid
methionine, slides into the P slot, and the anticodon and codon bases hydrogen
bond. The second codon is under the A slot. The second tRNA that recognizes
the second codon slides in. This puts the two amino acids, methionine on the first
tRNA and what ever is on the second, next to each other. The ribosome then
catalyzes the formation of a peptide bond between the two amino acids. The first
amino acid is released from the tRNA, and is now bound to the second amino
acid.
After the peptide bond forms, the ribosome slides along the mRNA by one codon.
The first tRNA, which is now empty, is in the E slot where it drifts away. The
two amino acid peptide chain is in the P slot. The A slot is empty, and ready for
the next tRNA to enter carrying the third amino acid in the chain. When it enters,
the ribosome peptide bonds it to the earlier amino acids. Then the ribosome
moves along the mRNA, reading the next codon. This continues until a stop
codon is reached. This stop codon is read by a tRNA that does not have an amino
acid attached. The ribosome tries to make a peptide bond, but it cannot. The
ribosome then aborts translation and releases the new protein so that it can fold
into its final shape.
XXXIV. Where does meiosis occur in humans? Mitosis? What are the differences
between mitosis and meiosis?
Meiosis only occurs in reproductive cells: the testes or ovaries. Mitosis occurs
everywhere in the body. The role of mitosis is to produce a perfect copy of a
cell—for humans, this is for growth and repair. Meiosis produces haploid
gametes (sperm/pollen or eggs), so that sexual reproduction can occur. It
produces haploid cells by going through two divisions: the first separates
homologous chromosomes; the second separates the identical sister chromatids
that were copied in S phase.
XXXV.
Describe the human genome, including the chromosome make up.
The human genome is about 3.2 billion bases of DNA. It is stored in 46
chromosomes, which can be broken down into 23 homologous (nearly identical)
pairs (one member of each pair comes from each parent). 22 pairs are autosomes;
the final pair may or may not be homologous—these are the sex chromosomes.
In humans, XX is female, and XY male. The Y chromosome is very small and
not essential for life.
XXXVI.
How do disorders like Turners, Klinefelter’s, and Down syndrome occur?
Turners (X-), Klinefelter’s (XXY), and Down syndrome (trisomy 21) result from
nondisjunction in meiosis. Both chromosomes in the homologous pair are dragged
into one cell in Meiosis I. This results in one cell having one too many
chromosomes, and the other missing that chromosome completely.