Molecular and Human Genetics

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Molecular and Human
Genetics

AP Biology Rapid Learning Series
Wayne Huang, PhD
Andrew Graham, PhD
Elizabeth James, PhD
Casandra Rauser, PhD
Jessica Habashi, PhD
Sara Olson, PhD
Jessica Barnes, PhD

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© Rapid Learning Inc. All rights reserved.

© Rapid Learning Inc. All rights reserved. :: http://www.RapidLearningCenter.com

1


Learning Objectives
By completing this tutorial, you will learn about:

Structure and Function of
DNA
Structure of RNA
Protein Synthesis
Molecular Genetics: Northern
Blot, Southern Blot, and DNA
,
,
Cloning
Human Genetics

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Concept Map
Molecular
Genetics

Genetics

Structure and
Function of DNA
Structure
of RNA

Human
Genetics

tRNA
mRNA
Karyotype

Sex-linked
Traits
Functional Protein
Synthesis

rRNA

Protein
Translation

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2


Structure and
Function of DNA
Molecular Genetics, DNA

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Molecular Genetics
Molecular genetics is a
division of biology that is
involved in the study of gene
structure and function.

The study of gene structure
has lead to a further
understanding of certain
p
,
disease processes, as well
as potential gene therapies.

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3


Cell Nucleus
The cell nucleus is usually near the center of the cell; it contains the
majority of the genetic material in a cell. Within the nucleus, the DNA is
compacted and organized into chromosomes. Also within the nucleus is
the nucleolus. The nucleolus has no true membrane surrounding it, and
this is where ribosomes are produced
produced.

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The cell nucleus is surrounded by a nuclear envelope, which contains
pores to limit flow in and out of the nucleus. The pores allow small
water-soluble molecules to diffuse into the nucleus but prevent large
molecules, such as proteins, from randomly entering the cell. The
outside of the nuclear membrane is continuous with the endoplasmic
reticulum and the attached ribosomes.

Question: Challenge

Define, in general, what the nuclear envelope is.

The cell nucleus is usually near the center of
the cell; it contains the majority of the
genetic material in a cell. The cell nucleus is
surrounded by a nuclear envelope, which
contains pores to limit flow in and out of the
t i
t li it fl
i
d
t f th
nucleus. The pores allow small water-soluble
molecules to diffuse into the nucleus but
prevent large molecules, such as proteins,
from randomly entering the cell.

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4


Nucleic Acids: DNA
Deoxyribonucleic acid (DNA) is the blueprint of life; it is present in
almost every cell in the body. A copy from a male donor and a copy from
a female donor, through fertilization, can create a human being.
Structurally,
Structurally DNA is made up of 2
polymers of nucleotide in a
complementary-based pair double helix.
These anti-parallel strands run in
opposite direction from one another and
are held together through hydrogen
bonds.
The structure of the double helix provides
a major groove in which transcription
factors can bind and impact gene
expression. The four different DNA
nucleotides follow a strict base pairing
arrangement: Guanine – Cytosine (3
hydrogen bonds) and Adenine – Thymine
(2 hydrogen bonds).

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Genetic Code
The genetic code dictates nucleic acid structure and function. The formation
of the end-product amino acids and proteins is controlled by the genetic
code set of rules. Within the code are codons, which are a nucleic acid
sequence that specifies the formation of an amino acid.

The genetic code allows
for more than one codon
to specify an amino acid.
However, there is no
ambiguity, as each
codon specifies only one
amino acid, depending
on the reading frame or
the context each codon
is read in.
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5


Semi-Conservative DNA Replication
DNA replication must take place in order for a cell to divide during mitosis.
During DNA replication, the parental DNA is separated and each parent
strand acts as a template for the formation of a new complementary strand.
This is known as semi-conservative DNA replication. Each daughter cell
receives one strand from the parental cell DNA, along with its one entirely
i
df
h
l ll DNA l
i hi
i l
new strand.

11/35

Question: Challenge

Define, in general, what the genetic code is.

The genetic code dictates nucleic acid
structure and function. The formation of the
end-product amino acids and proteins is
controlled by the genetic code set of rules.
Within the code are codons, which are a
nucleic acid sequence that specifies the
formation of an amino acid.

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6


RNA and Protein
Synthesis
Structure of RNA, Protein Synthesis
y

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Nucleic Acids: RNA
Ribonucleic acid (RNA) is usually singlestranded. It is made from a DNA blueprint. RNA
translates the message from the DNA to produce
the correct protein. The different types of RNA
include:
(1) Messenger RNA (mRNA) – binds to ribosomes
and provides the template for protein translation,
(2) Transfer RNA (tRNA) – transfers a specific
amino acid to the growing polypeptide protein at
g
g p yp p
p
the site of translation, (3) Ribosomal RNA (rRNA )
– the central component of the ribosome. It
decodes messenger RNA and provides the actual
binding site for the incoming tRNA.

14/35


7


RNA Transcription
Genes drive protein synthesis in the
following manner: DNA is
transcribed into RNA, and then RNA
is translated into proteins. RNA is
produced by an enzyme known as
d
db
k
RNA Polymerase.
RNA polymerase transcribes a
complementary base-paired RNA strand.
During the base pairing, Uracil is
substituted in the growing RNA strand for
Thymine. The RNA strand produced by
this process is known as messenger RNA
(mRNA). The process involves initiation,
elongation of the transcript, and
termination; it takes place in 5ʹ to 3ʹ
direction. Only 1 DNA strand (template
strand) is transcribed and, due to the
complementary base pairing, the original
instructions of the DNA are carried out.
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Types of RNA
There are three types of RNA: (1) Ribosomal
RNA (rRNA) – ribosomal RNA is the central part
of the ribosome, along with its associated
proteins. rRNA decodes messenger RNA into the
individual amino acids.
acids
(2) Transfer RNA (tRNA) – transfer RNA
contains an anti-codon region, which interacts
with the appropriate codon on messenger RNA
to ensure the proper amino acid is added to the
growing protein. Transfer RNA has a single
amino acid, which transfers to the growing
g
g
protein.
3) Messenger RNA (mRNA) – messenger RNA is
the blueprint necessary for protein production. It
binds to the ribosome and provides the codon,
which is matched with the anti-codon of tRNA.
This ensures the protein is assembled in strict
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accordance with the DNA template.


8


Question: Challenge

What are the 3 types of RNA?

(1) Messenger RNA (mRNA) – binds to
ribosomes and provides the template for
protein translation, (2) Transfer RNA (tRNA) –
transfers a specific amino acid to the
g
growing polypeptide protein at the site of
g p yp p
p
translation, (3) Ribosomal RNA (rRNA ) – the
central component of the ribosome. It
decodes messenger RNA and provides the
actual binding site for the incoming tRNA.

17/35

Protein Translation
Protein translation is the process whereby amino acids are
assembled into a polypeptide chain or protein, based on
the DNA code. The process involves the following steps:

(1) Initiation – Once the ribosome is assembled,
initiator tRNA, carrying methionine, binds to the
start site on the mRNA.

(3) Termination – Translation
stops when one of three
termination codons moves
into the A site on the mRNA.
Release factors trigger the
18/35
release of the new protein.

(2) Elongation – After the initiator tRNA is bound
to the P site the next tRNA is able to bind to the
site,
A site. Amino acids are added to the growing
polypeptide chain by forming a peptide bond
with the previous amino acid. Next, the mRNA is
shifted by one codon, freeing up the A site to
receive the next amino acid.


9


Molecular Genetic
Techniques
Cell Culture for Nucleic Acid Samples, Northern
p
Blot and Southern Blot

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Tissue Cell Culture
Tissue culture is the process of growing cells and established cell lines
in a controlled environment. Cells are grown in specific media,
containing the necessary nutrient supplements and additives, such as
hormones and growth factors.

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Cells are grown in flasks, coated plates with
individual wells, or in petri dishes. Most cells
can be maintained in log phase growth by
replacing the growth media when needed and
storing the cells in humidified incubators at
37°C – to simulate body temperature.


10


Nucleic Acid Extraction
After cells are harvested by enzymatic digestion, they are prepared for
nucleic acid extraction. First, the cells are broken or lysed, and then
detergents and proteases are used to remove membrane lipids and
unwanted proteins. For extracting DNA, graded alcohol solutions are
proteins
DNA
used to precipitate the DNA out of solution. To detect DNA, light
absorption spectroscopy can be used.

Extracting RNA from cells requires the deactivation of
ribonuclease enzymes, which would degrade the RNA
sample. Usually, this takes place in the lysis buffer
when the RNA extraction begins.

21/35

RNA Extraction: Northern Blot
The Northern Blot technique
allows the experimenter to
detect and study the RNA
from cells. In general, total
RNA is extracted from cells,
cells
and then mRNA can be
isolated to study gene
expression.

22/35

Once the RNA sample is extracted from the cells or tissue, it must be
separated to probe for the RNA of interest. RNA can be separated using
gel electrophoresis. Gel electrophoresis involves applying a current to a
gel matrix containing the RNA sample. RNA samples move through the
gel and separate into bands based on their charge to mass ratio. After
separation, they can be transferred to a blot membrane and probed for
the RNA of interest using a specifically labeled probe.


11


DNA Extraction: Southern Blot
A Southern Blot is a technique to study the presence and levels of
DNA sequences in cells under certain conditions. Similar to Northern
blots, after the DNA is extracted from the cells, it is usually separated
using gel electrophoresis.

After i
Aft using a specific probe to
ifi
b t
identify the DNA of interest, the
results appear as bands. The
bands are a result of
autoradiography or other
detection methods.
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Gene Cloning
Gene cloning can be used to create many copies of a defined DNA
sequence. The sequence of DNA or gene can then be used to test the
effect of over-expression or deletion of that gene from the genetic
material of cells.

First, the DNA sequence of
interest must be isolated.
Next, the sequence is
typically ligated into a
plasmid, which then is
used to transform the
target cell or bacteria for
gene production.

24/35


12


Question: Challenge
Define, in general, the method used to extract
and investigate the DNA in cells.
g

A Southern Blot is a technique to study the
presence and levels of DNA sequences in
cells under certain conditions. Similar to
Northern blots, after the DNA is extracted
from the cells it is usually separated using
cells,
gel electrophoresis. After using a specific
probe to identify the DNA of interest, the
results appear as bands. The bands are a
result of autoradiography or other detection
methods.
25/35

Human Genetics

Karyotype, Population Genetics, and Genetic
y yp
p
Counseling

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13


Karyotype
Cytogenetics involves the study of chromosomal abnormalities and
deficiencies. As part of these studies, a karyotype is prepared. A karyotype
is a visual pattern of the chromosomes within cells. By using stains and
probes, whole chromosomes, short and long arms, and even small regions
on chromosomes can be visualized.
visualized

Normally, there are 22 pairs of autosomes and 1 pair
of sex chromosomes, for a total of 46. Karyotypes can
reveal the sex of the individual, as well as more finite
details of the health. An example would be Down
Syndrome, which is evidenced by 3 copies of all or
27/35
part of chromosome 21.

Sex-Linked Traits: X-Linked
For example: A gene (e.g. hemophilia) is
recessive and located on the X
chromosome; this is the inheritance
pattern for that gene.

X-linked means
the gene of a
particular trait
resides on the X
chromosome.
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14


Y-Linked Traits
Y-linked traits appear only in
males and are only passed from
father to son.

Males contribute either an X or Y
chromosome during fertilization. If
an X chromosome is contributed,
the genotype will be XX female; if a
Y is contributed, the genotype will
be XY, resulting in male offspring.

Y-linked genes
reside only on the
Y chromosome.
There are very few
Y-linked traits.
traits

A pedigree of Ylinked traits

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Population Genetics
The study of gene allele frequency distribution across a population is known
as population genetics. This type of study addresses changes in
populations, such as adaptation and speciation. The frame work of
population genetics, involving the mapping of a set of genotypes to a set of
phenotypes,
phenotypes is called a genotype-phenotype map.
map

Genotype-phenotype maps can depict
changes in phenotype or morphology, even
though the genotype is very similar or
identical in some cases.
30/35


15


Genetic Counseling
Genetic counselors discuss and advise patients about the risk of
potential inherited disorders. The likelihood of disease transmission in
children and the effects of the inherited disease or disorder are
presented.

In the USA, genetic counselors are trained
in genetic disease outcomes, possible
treatments, and heritability. This education
is in addition to their previous biology,
psychology or medical background. They
are certified by the American Board of
Genetic Counseling.

31/35

Question: Challenge
What is the inheritance pattern of a Y-linked
trait?

Males contribute either an X or Y
chromosome during fertilization. If an X
chromosome is contributed, the genotype
will be XX female; if a Y is contributed, the
genotype will be XY, resulting in male
offspring. Y-linked traits appear only in
males and are only passed from father to
son.
32/35


16


Learning Summary
Genetic
counselors
discuss and
advise patients
about the risk of
potential inherited
disorders.

The cell nucleus is
usually near the
center of the cell;
within the nucleus,
ithi th
l
the DNA is
compacted and
organized into
chromosomes.

The genetic code dictates
g
nucleic acid structure and
function. The formation of
the end-product amino acids
and proteins is controlled by
the genetic code set of
rules.

RNA is usually
single-stranded. It is
made from a DNA
blueprint.
blueprint RNA
translates the
message from the
DNA to produce the
correct protein.

Y-linked traits appear only
in males and are only
passed from father to son.
Y-linked genes reside only
on the Y chromosome.
There are very few Y-linked
traits.

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Congratulations
You have successfully completed
the tutorial

Genetics I: Molecular and
Human Genetics


17


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Molecular and Human Genetics

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