GENE STRUCTURES

High School Biology Rapid Learning Series - 11

Rapid Learning Center
Chemistry :: Biology :: Physics :: Math

Rapid Learning Center Presents …
p
g

Teach Yourself
High School Biology in 24 Hours

Ge e St uctu es
Gene – Structures
and Functions
High School 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

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

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

1


Learning Objectives
By completing this tutorial, you will learn about:
DNA: Chemical
Composition and Structure
Genes: the Genetic Code
and the Central Dogma
How genes are inherited
Mutations and Genetic
Disease
Gene Therapy

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Concept Map
DNA

Replication

DNA
Transcription

Daughter
cell

Transcription
mRNA

rRNA

Assembly

tRNA
Translation

Assembly
Amino acids

Ribosomes
Assembly

Protein

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2


DNA Structure
Chemical composition of DNA
Physical structure of DNA
DNA organization in cells
Relationship between DNA and genes.
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DNA and You
Genes dictate your phenotype.

Your face
Your weight

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Your height

Disease susceptibility


Rate of aging

3


DNA Basics
Genes are considered as the
unit of genetic inheritance.

DNA (deoxyribonucleic
acid) is made up of genes.
Genes code for the
p y
physical development and
p
phenotype of an organism.

Chromosomes are
C
made up of genes and
are associated with
proteins. They are
located in the nucleus.

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The Building Blocks of DNA
Nitrogenous Bases

Guanine

Adenine

Thymine

BASE

Cytosine

Glycosidic Bond

Deoxyribose

Nucleoside

Nucleotide monophosphate
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Phosphate Base

+ Deoxyribose +

Nitrogenous
Base


=

Deoxyribonucleic
Acid

4


Chemical Composition
Four bases make up DNA: Adenine (A),
guanine (G), cytosine (C) and thymine (T).
A only pairs with T and G on pairs with C in
DNA.
DNA has a phosphate backbone.

Backbone
Bases

AT G C C T G AC T T T G T G
T AC G G AC T G AAACAC

Backbone

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Putting the DNA Blocks Together
Nitrogenous Bases
Phosphate

5

Deoxyribose

3

DNA Nucleotides are
linked at their
phosphate groups in a
phosphodiester bond.

Notice the phosphate
bonds are formed at the
5’ and 3’ positions.
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5


Purine and Pyrimidine Nucleotides

(Adenine A)
(Guanine G)

Deoxyadenosine 5'-phosphate (dAMP)

Deoxyguannine 5'-phosphate (dGMP)

(Cytosine C)

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Deoxycytosine 5'-phosphate (dCMP)

(Thymine T)

Deoxythymine 5'-phosphate (dTMP)

DNA Strands are Antiparallel
The arrangement of the components of DNA

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6


RNA DNA Structure Comparison
Major Differences between RNA and DNA:

Base:
Sugar:
S
3D Structure:

DNA
A, T, G, C
Deoxyribose
D
ib
Long, Double Helix

RNA
A, U, G, C
Ribose
Rib
Various Conformations

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Organization of DNA in the Cell
DNA is highly organized into chromosome within cells.

DNA strands
Double Helix
Nucleosome
Chromatin
Chromosome

Chromosome
(in cell nucleus)

14/52


7


Gene Basics
Genes are sections of the DNA
that code for a protein.
There are many genes within a
DNA or chromosome molecule.

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This is chromosome 16. Notice
the stripes which indicate genes.

90 million base pairs are contained in this
chromosome and dozens of genes.

Gene to Protein
Gene translation and transcription.
Genetic code for protein sequence.
sequence
Central Gene Dogma
Proteins, amino acids and basic structure.

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8


DNA to mRNA to Protein
DNA → mRNA → Protein
mRNA transcript is
exported from the
nucleus to the cytoplasm

Amino acid added to
growing protein chain.

Newly formed
peptide chain

Amino acid
tRNA
mRNA
ribosome

tRNA binding
to codon

Completed protein
Translation at the ribosome level
Start of
polypeptide chain

Maturing
protein

Cytoplasm

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ribosomes
mRNA

Transcription

Translation

Different Types of RNA
mRNA carries the information
for the amino acid sequence
of a polypeptide (protein)
chain.

tRNA carries amino acids to
the ribosome and transfers
them to the growing
polypeptide chain.

rRNA are pieces of RNA
that form complexes with
ribosomes (protein) to
facilitate the transfer of
amino acid from tRNA to
the polypeptide chain.

snoRNAs small nuclear
RNAs used to process
and chemically modify
rRNAs.
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snRNA forms complexes
with proteins used in
eukaryotic RNA processing
(e.g. exon splicing and
intron removal).

9


Types of RNA
mRNA encodes the
amino acid sequence of
a polypeptide and is
copied from DNA.

tRNA: transfer RNA, transports
amino acids to the ribosomes
during translation.

rRNA: ribosomal RNA forms
complexes with ribosomal proteins
and is essential for the translation
of the mRNA sequence.
snRNA: small nuclear RNA
forms complexes with
proteins used in eukaryotic
RNA processing, e.g. exon
splicing, intron removal.

snoRNAs: small nucleolar
RNAs guide chemical
modification of rRNAs and
other RNA genes (tRNAs,
snRNAs). They are classed
as snRNA.

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Three Steps to RNA Synthesis

Termination

Elongation

Termination, elongation
and initiation of RNA
synthesis occurs in
prokaryotes and
eukaryotes.

Initiation

Elongation is the same
in
i prokaryotes and
k
t
d
eukaryotes but
initiation and
termination differ.

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10


DNA is Transcribed to mRNA
DNA transcription begins with
the unwinding and opening of
the DNA double helix.

Ultimately the mRNA is
exported from the nucleus to
the cytoplasm for translation
into a protein.

A mRNA molecule
complementary to the
DNA sequence is made.
21/52

Transcription
RNA copies information from DNA template through baseparing mechanism, UA/AT or CG/GC.

DNA Template
(one strand)

A T G C C T G A CA T T G T G
Transcription

Transcription

UA C G G A CUGUA A C A C
RNA product

22/52


11


RNA Synthesis Process
RNA synthesis is
regulated by gene
regulatory elements
within each gene.

RNA polymerase unwinds the DNA and
RNA is transcribed 5’ to 3’ from the
DNA template (3’ to 5’).
RNA synthesis is similar to DNA
synthesis with these exceptions:
NTPs not dNTPs are used and there
is no primer.
Uracil instead of thymine is used.

And an RNA polymerase
is used instead of a DNA
polymerase.
23/52

Processing of mRNA
In post transcriptional
modification precursor
mRNA from eukaryotes are
converted into mature mRNA
(this is not post translational
modification).

1. 5’cap occurs
while the RNA
molecule is being
transcribed after
about 30 nucleotides
have been added.

24/52

The three main modifications
are 5’capping, 3’
polyadenylation and RNA
splicing.

3. RNA splicing: introns (regions
of RNA that do not code for
protein) are removed from the premRNA leaving exons connected.
The splicing is catalyzed by a large
protein complex called the
spliceosome. There are many
ways to splice a mRNA allowing for
a large variety of proteins from a
limited amount of DNA.

2. Cleavage of the 3’ end is followed by
adding polyadenosine (poly-A) tail.


12


Transcription Termination
Prokaryotes and Eukaryotes have different
mechanisms to stop transcription.
Eukaryote transcription
termination is not
completely defined but
seems to involve the
cleavage of the nascent
transcript, followed by
template-independent
addition of A’s at the new 3’
end. This is called Polyadenylation.

Bacteria use two kinds of RNA
transcription termination strategy:
t
i ti
t
i ti
t t
“Rho independent” type stops
transcription when the RNA
molecule forms a hairpin loop
structure followed by a whole
bunch of uracil bases.

25/52

Protein Basics
There are 20 amino
acid residues. The
amino acids are
joined together by
a peptide bond.

The amino acid
sequence of a protein
is determined by the
DNA sequence of the
gene.

Typically one
gene encodes for
one protein. This
is called the one
gene one protein
hypothesis.
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13


Introduction to Amino Acids
Do you know what an
amino acid is?

Yes, an α amino acid has a
central carbon atom,
called an α carbon.

Amino acids also
have an amino and
carboxylic acid
group.

And an H and
R group
27/52

Protein Basics
The protein sequence is
determined by the DNA
sequence of the gene.

The sequence of amino
acids is called the
primary structure of a
protein.

Gene

Protein (Gene Product)

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14


The Central Dogma
How are genes converted into its final functional product?
DNA
DNA replication
Transcription
mRNA

Translation

tRNA, rRNA, non-coding RNA

Protein

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The Genetic Code
DNA is made up of: Adenine, Guanine, Cytosine and
Thymine.
A codon is a three nucleotide sequence that codes for
an amino acid.
There are three codons that signal stop transcription.

Codons
Amin
o
Acid

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15


Protein Biosynthesis Three Phases
There are three phases in
protein biosynthesis. Who
knows what they are?

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The Genetic Code
mRNA is read in a sequential
manner starting from a fixed point
(initiation codon, AUG) and
stopping at stop codons.
Every three bases on mRNA
determine one amino acid (triplet
code).
Each of 64 combinations (43) of
triplet bases encodes an amino
acid or a stop codon.
One amino acid may be encoded
by multiple codons .
The amino acid sequence is said to
be degenerative because there are
64 codons for 20 amino acids.
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16


Protein Biosynthesis - Elongation
Elongation:

Incorporation of an Amino Acid Into a Protein
Peptidyl tRNA attached to
C-terminal of the growing
Polypeptide chain

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DNA Replication

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17


3-Step Replication Process

Initiation
Elongation
Termination

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Transmission of Genes
Cell division and DNA Replication

A new cell derives its DNA
from an older cell
An older cell prepares an
extra set of DNA copies to
give to its daughter cells
(DNA replication)
The duplicated DNA is
separated evenly into two
daughter cells, with each cell
containing one complete set
of DNA
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18


DNA Replication - Definition
The process of making an identical copy of a section of
duplex (double-stranded) DNA, using existing DNA as a
template for the synthesis of new DNA strands.

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Semi-Conservative DNA Replication
A parent DNA molecule
is replicated
replicated.

Original Parent Molecule

One parent strand is in each
of the two new molecules.

First-generation daughter molecules
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19


DNA Replication Process
The parent double helix opens and a complementary
daughter strand synthesized.

Newly Synthesized
Strands

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The product of semi conservative replication is two double
helices each having one new strand and one parent strand.

Initiation of Replication
DNA strands separate at the origin
and replication proceeds in
opposite directions along the DNA.

At the origins of replication
a replication fork emerges
opening the double helix.

DNA replication is bidirectional.

40/52

The strands are primed and replication
proceeds from, the 5’ to 3’ direction.


20


Lagging Strand Replication
In DNA replication the lagging strand is the strand
opposite of the replication fork of the leading strands.
Replication is in the 3’ to 5’ direction.

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1. On the lagging strand primase reads the DNA and adds RNA sequences to
act as a primer for POL III DNA polymerase. Multiple RNA primers needed.
2. Pol III lengthens the primers forming Okazaki fragments.
3. Pol I then removes the RNA and adds its nucleotides.
4. DNA ligase joins the fragments.

Leading Strand Replication
The leading strand is done in a single unit
not fragments as it is in the lagging strand.
Replication is in the 5’ to 3’ direction.

42/52

Helicases are enzymes that
move directionally along a
nucleic acid phosphodiester
backbone separating two
annealed nucleic acid strands.

1. On the leading strand Pol II reads the DNA and adds nucleotides
continuously.
2. On the leading strand DNA polymerase III is able to synthesize DNA using
free 3’OH group donated by a single RNA primer.
3. Continuous synthesis occurs in the direction the replication fork is moving.


21


Fidelity of DNA Replication
Mutations
Genetic Diseases
Gene Therapy

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DNA Mutations & Heredity
A gene mutation is a permanent change
in the DNA sequence that makes up a
gene.

DNA Mutant Gene
and Inheritance

Gene mutations occur in two ways:
they can be inherited from a parent
acquired during a person’s
lifetime.
Acquired (or somatic) mutations occur
in the DNA of individual cells at some
time during a person’s life due to
environmental factors.
Acquired mutations in somatic cells
cannot be passed on to off spring.
Mutations that are passed from parent
to child are “hereditary mutations” or
“germline” mutations.
Mutations that are only in egg or sperm
or those that happen immediately after
fertilization are “de novo” mutations.
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22


5 Basic Types of Mutations
These are the five basic DNA mutations.

Deletion Mutation

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Duplication Mutation

Inversion

Translocation

Insertion

Causes of Mutations
“X” Incorrect
nucleotide inserted.
X

DNA damage caused by
radiation, UV exposure or
mutagenic chemicals.

Errors during DNA replication

Chromosome translocation,
deletion, duplication and inversion

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There are many other causes of DNA
mutations, including environmental
and genetic instability.


23


Results of Mutations
Silent mutations have a DNA
base change but this change
does not result in a different
amino acid in the protein.

Missense mutation is a DNA
base change resulting in the
insertion of a different amino
p
acid in the protein.

Nonsense mutations code
for a stop where one
should not be. This results
in a truncated protein.

47/52

Gene Therapy
Gene therapy may be used to fix a
damaged gene or insert a new one.
First a piece of DNA having the normal or new gene is isolated.

The gene is inserted
into a vector. A
vector can carry the
new gene to the
target cell.

Vector-DNA
complex infects
target tissue.
48/52


Replication of new gene
begins and protein is
synthesized.

24


Question: Review

___________
DNA

Phosphate base + deoxyribose
+ nitrogenous base =
Purine bases include ______
and _____.

Segments of DNA that code
for a protein are called ____.

___________
Genes

DNA replication is _______.

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___________
Adenine, guanine

___________
Semi-conservative

Gene mutations happen in
two ways. What are these
ways?

Inherited or acquired

___________

Learning Summary
DNA → mRNA →
Protein
DNA is transcribed to
mRNA.
mRNA is translated to
protein.

Result of DNA
mutations include:
1. Silent mutation.
2. Missense.
3. Nonsense.

DNA Bases
A:T adenine always
pairs with thymine
G:C guanine pairs
with cytosine.

5 Types of Mutations
yp
1. Deletion
2. Duplication
3. Inversion
4. Insertion
5. Translocation

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25


Congratulations
You have successfully completed
the core tutorial

Gene – Structures and
Functions
51/52

Chemistry :: Biology :: Physics :: Math

What’s N t
Wh t’ Next …
Step 1: Concepts – Core Tutorial (Just Completed)
Step 2: Practice – Interactive Problem Drill
Step 3: Recap – Super Review Cheat Sheet
Go for it!

52/52

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GENE STRUCTURES

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