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Biology Review: Answers
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1. Label the diagram of the cell below. Describe the function of each of the
structures.
a. Cell membrane – controls entry and exit of molecules into and out of the
cell.
b. Vacuole or vesicle: storage container
c. Smooth endoplasmic reticulum – transports proteins (as well as other
things)
d. NUCLEOLUS! – site of ribosome production
e. Centrioles – involved in cell division and the production of the spindle fibres
f. Golgi apparatus- receives proteins from the ER, repackages them and then
sends them to where ever they were destined to go.
g. Nucleus – stores the DNA and contains the nucleolus
h. s Mitochondria – site of cellular respiration (releases the Energy from the
glucose molecule for the cell to use)
i. Cytoplasm – bathes the organelle
j. Ribosomes – site of protein synthesis
k. Lysosomes – vesicles filled with digestive enzymes. Used to digest food
vesicles and to clean up the cytoplasm from the waste and debris
l. Nuclear pores – openings in the nuclear membrane to allow substances into
and out of the nucleus
m. Rough endoplasmic reticulum (ER covered in Ribosomes) transport the
proteins produced by the ribosomes to locations throughout the cell.
2. What does the DNA molecule give instructions for (specifically)? Why do we call
this our “blueprints”? The DNA molecule is a recipe book for PROTIENS. We
call this our blueprints because once we know how to make proteins, they can
work as enzymes. Enzymes control ALL our chemical reactions in our body,
and ALL we consist of is a very highly controlled, specific series of chemical
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Biology Review: Answers
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reactions. When our enzymes die, so do we, and all our building blocks go back
to the earth to be reused for some other organism.
3. What do we call a portion of the DNA molecule that codes for one protein?
We call one portion of our DNA that codes for one protein a gene. We have
thousands of genes in our entire genome.
4. What is the difference between chromatin, chromosomes, and chromatids?
Chromatin is the indistinguishable mass of DNA molecules that exist in the
nucleus during the normal lifetime of the cell. At the time of cell division, the
chromatin duplicates and organizes into chromosomes. Chromosomes consist of
two chromatids attached together with a centromere. Because of this structure, the
chromosomes resemble the letter X when you see them under a microscope. The
chromatids are separated during anaphase – one copy going north and the other
copy moving south.
5. What is cancer? What causes cancer? Cancer is uncontrolled cell division.
Normally, cells divide in a very coordinated and organized manner. Cancer
cells have lost all of this control, and therefore will often cause a lump or mass
wherever it occurs. Cancer is caused by MANY things, but all cancers are the
result of genetic mutations – the rearrangement of the genetic code inside the
nucleus. The mutations usually occur in the genes that code for enzymes that
are responsible for cell division control. This code can be altered by radiation,
chemicals or just a mistake when the cell is reproducing.
6. What is a mutation? A change in the sequence or structure of the DNA
molecule. It can be negligible, advantageous or deleterious. It usually causes a
change in the protein that was being coded for at that location of the change in
the DNA.
7. How can chemicals cause mutations? Chemicals can react with the DNA
molecule, changing it’s structure and hence changing the sequence of the
nucleotides. When you change the DNA code, a mutation occurs.
8. How can radiation cause mutations? Radiation can physically break the DNA
molecule and disrupt the chain of nucleotides, causing a mutation.
9. What is the difference between positive, neutral and negative effects of various
mutations? Positive mutations actually improve the functioning of the enzyme
that is produced after the change. Neutral mutations are changes in the
nucleotide sequence that do not affect the function of the enzyme produced by
that gene. Negative mutations cause the enzyme to work poorly, or sometimes,
not at all. This has a negative affect on the cell and possibly the organism.
10. What is gene therapy? Gene therapy is an experimental procedure that treats
genetic disorders by replacing the mutated/dysfunctional genes with a healthy
copy of the genes. It is VERY difficult, but researchers are confident that the
technique will become successful in the future.
11. Draw a section of the DNA molecule. Label all of the parts, including nucleotides,
phosphates, sugars, nitrogenous bases, sense strand, and anti-sense strand. What
structures are considered the “backbone” of the molecule? The “rungs” of the
ladder? The “backbones” are the sugar and phosphate down the sides, and the
“rungs” of the ladder are the nitrogenous bases.
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Biology Review: Answers
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12. What part of the DNA molecule carries the code? The sequence of the
nucleotides gives the actual code. Specifically, it is the nitrogenous bases within
the nucleotides that determines the code. On a structure diagram, these are
often called the “rungs of the ladder”.
13. Describe how the code works by comparing it to a sentence. In our genetic code,
we only have 4 “letters” to the “alphabet”– the nitrogenous bases adenine (A),
guanine (G), Cytosine (C) and Thymine (T). (in the mRNA copy, Uracil (U)
replaces thymine). Words are constructed from the sequence of the bases, and
are ALWAYS 3 letters (bases) long. These words are called triplets or codons.
The words are translated into specific amino acids. There are only 20 amino
acids, so there are often 3-4 codons that translate to the same amino acid.
“Sentences” begin with the code AUG – which translates into the amino acid
methionine. This means “start”. The sentences end with a stop codon – UAA,
UAG, or UGA. Sentences usually translate enough amino acids in a chain to
form one protein molecule. We call the “sentences” genes. Usually, one gene =
one protein.
14. Decode this piece of mRNA: AUG UUU CCA GGC GAC UGA (a code will be
provided on the test) met. (start) – phe – pro – gly – asp - stop
15. What does methonine also mean? Start