Download Chapter 13: DNA Within the of almost all of your cells 46 DNA

Chapter 13: DNA
Within the _________________ of almost all of your cells 46 DNA molecules
or chromosomes contain approx. 20-25000 genes. These genes act as a
_________________ directing which proteins are to be synthesised by the
cell. By controlling cell _________________, DNA is able to determine the
characteristics of a person. DNA is unique among molecules because its
structure allows it to manufacture another molecule, _________________ to
itself, and in doing so transmit its _________________ code from parents to
their children and from one cell to another as new cells are formed.
DNA is a condensation _________________ constructed from four monomers
known as nucleotides. Each nucleotide consists of a phosphate group, a
deoxyribose sugar group and one of the four bases. The four bases are
adenine (A), _________________ (C), thymine (T) and _________________ (G).
Adenine and Guanine are derivatives of the organic compound purine
and as a results are referred to as _________________ bases. Cytosine and
thymine are derivatives of another compound, pyrimidine, and are
referred to as _________________ bases. The base forms a covalent bond to
the carbon atom labelled C1 in the _________________ molecule. The
phosphate group bonds to the carbon atom labelled C5. A water
molecule is produced when each bond is formed.
Draw the four bases
Primary Structure
_________________ bonds are responsible for producing the primary
structure of DNA. A covalent bond is formed between the 5’-phosphate
group on one nucleotide and the 3’-_________________ on the deoxyribose of
another. One end of the DNA strand has a hydroxyl group and is called
the 3’ end. The end of the _________________ with the phosphate group is
called the 5’ end. In this way, _________________ undergo condensation
polymerisation to form a long chain of nucleotides. A base is also
covalently bonded to the sugar group at the C1 site via a _________________
reaction. It is the sequence of bases along the _________________ -phopshate
backbone that forms the _________________ structure and is the basis for
the genetic code.
Secondary Structure
As is the case in proteins, _________________ bonding is responsible for
maintaining the secondary structure of DNA. For a given species, the
percentage of each of the four bases is the same in all cells and is
characteristic of the organism. The mole amounts of _________________ (a
purine) and adenine (a _________________) are equal. The mole amounts of
cytosine (a pyrimidine) and _________________ (a purine) are equal.
By considering the _________________ of the base pair A and T, it can be
seen that they are able to fit together. It is possible for two hydrogen
bonds to form between the _________________ negative on the nitrogen and
oxygen atoms and the dipole positive on hydrogen atoms on the
_________________ base. With base pairs C and G three hydrogen bonds can
form between the nitrogen and _________________ atoms of one base and
the hydrogen atoms on the adjacent base.
The secondary structure of DNA is a pair of DNA _________________ strands
held together by hydrogen bonding between the bases A-T and C-G. The
structure _________________ around to form a right-handed double helix.
The _________________ -phosphate backbone forms the handrails and the
pairs of bases the steps. The pairing of bases is referred to as
complementary base pairing. The _________________ strands align in
opposite direction.
Tertiary Structure
The _________________ groups in the backbone of the double helix give DNA
molecules a negative charge, and this enables the molecules to interact
with a group of proteins called _________________. The DNA molecules wrap
around histones and become _________________ coiled. This allows the DNA
to be very tightly and efficiently packaged, each molecule forming a
structure known as a _________________.
Replication
The _________________ of plant and animal cells involves a mechanism that
generates an exact copy of their DNA. The DNA double _________________
partially unwinds, as hydrogen bonds between the two DNA strands are
broken. Enzymes catalyse this process. The bases exposed on the
separated strands then act as a template to which new _________________
attach by hydrogen bonds between complementary base pair, C and G, A
and T. These _________________ then undergo a condensation
polymerisation reaction catalysed by the enzyme DNA polymerase to
form two exact copies of the original DNA _________________ helix.
Alternative sequences of nucleotides can occur at specific positions on a
given _________________. The alternative sequences are referred to as
alleles. Alleles give rise to most of the variation we see between people.
_________________ code – a sequence of three DNA bases codes for an amino
acid. RNA decodes the information on DNA in the nucleus of the cell
where protein synthesis takes place. Another type of _________________
controls the selection and sequencing of the amino acids that form
proteins.
Read Sickle-Cell Anaemia and Cystic Fibrosis
Electrophoresis
_________________ is an analytical technique, similar to chromatography,
that allows large charged molecules, DNA and proteins, to be separated
and quantitively determined. In electrophoresis the sample solution is
placed into a “well” in a block of conducting _________________ gel, sitting
between (+) and (-) electrodes.
_________________ ions, such as DNA fragments, in the sample move toward
the positive electrode. The rate of travel depends on their size, how
many base pairs there are. For DNA analysis, the sample “well” is placed
near the negative electrode, as DNA fragments, with their
_________________ phosphate linkages, are always negatively charged. The
distance the fragments move is compared against the distance travelled
by known standards. The separated components can be made visible by
adding fluorescent dyes or _________________ markers.
DNA Profiling
The sections of DNA that do not code for the production of
_________________, non-coding regions are more useful for forensic
scientists because they differ significantly from person to person. Of
particular interest is the _________________ of times a particular sequence
of bases may be repeated eg. on _________________ 5 the sequence AGAT is
repeated between 7 and 15 times, depending on the person. When you
examine 10 different chromosome sites, counting the number of base
sequence repeats, an accurate _________________ profile identification is
assured.
Polymerase Chain Reaction
A major problem with early DNA forensics was obtaining a big enough
biological sample, blood, skin, semen etc. to analyse. _________________ has
enabled forensic scientists to produce a DNA profile from an extremely
small sample. PCR utilizes DNA’s ability to _________________ itself, making
multiple copies of the sections of the DNA of interest. PCR involves 3
steps …
1. _________________ … heating breaks the H-bonding between DNA strands
2. _________________ … the sample is cooled and primers are added to bond
to the start and end of the base sequence to be copied
3. _________________ … the sample is warmed and polymerase enzyme
catalyst assists the addition of complementary base pairs and the
formation of H-bonds between the DNA strands
The amplified DNA _________________ are then separated using gel
electrophoresis and the analysis of the number of base sequence
repeats for 10 different _________________ locations performed
automatically.