Download Unit 3 * Molecular Genetics

Unit 3 – Molecular
Genetics
Lesson 1 – Intro to Genetics and DNA Structure
Central Themes

Some central themes that apply to this unit:

# 1 Living organisms are extremely diverse, but possess an underlying unity. For example,
many biochemical pathways found in bacteria are also present in human beings. Many other
aspects of cellular structure and function are universal among living organisms.

# 2 All organisms are capable of self reproduction based on a set of instructions known as the
genome. The genome in all cellular organisms is composed of DNA-a striking example of the
unity in diversity mentioned above.

# 3 Life as it exists today is the product of evolution: the change in the genomic composition
of populations of organisms over time. The course of evolutionary change is directed by
natural selection. Evolution by means of natural selection is the most important unifying
theme in biology. It explains the unity in diversity, the complementarities of structure and
function, and the adaptations to varying niches exhibited by life.
Learning Goals

Identify the monomer units of nucleic acids

Identify the two primary nucleic acid polymers, DNA and RNA, and particulars
about their structure.
DNA and You

Discuss the following questions with your table:

What are the potential benefits to knowing more about your genetic
predisposition (your chance of developing) to a disease?

What are the possible downsides to knowing?

Aside from health information, what else might you be curious to learn about
from your DNA?
Nucleic Acid

Nucleic acids are named as such
because they were originally found
in the nucleus of the cell and
contained phosphate groups (related
to phosphoric acid).
Nucleic Acid Monomers

Nucleic Acids are polymers. They are
made up of monomer units called
nucleotides. A nucleotide consists of
a phosphate, a pentose sugar, and a
nitrogenous base.
Nitrogenous Bases

There are (generally speaking) 5
different bases found in nucleic
acids.

Two double ringed purines:
Adenine and Guanine.

Three single ringed pyrimidines:
Thymine, Cytosine and Uracil.
Phosphodiester Bonds

Nucleotide monomers can be linked
together through a dehydration synthesis
that create phosphodiester bonds.

These bonds occur between the 3’
Carbon OH group of one nucleotide and
the 5’ Carbon Phosphate group.

How does this compare to other
polymerization reactions?
Orientation of Strand

Nucleic acid strands can be
described by the orientation of
the 5’ end (free phosphate) and
the 3’ end (free OH).

We can talk about an order of the
bases using this standard. Order
is typically denoted in a 5’ to 3’
direction.
Deoxyribosenucleic Acid

DNA is the most well known nucleic acid. It
stands for deoxyribonucleic acid.

DNA is double stranded with bases hydrogen
bonded to each other at the centre.

Strands run antiparallel to each other (in
opposite directions).

Bases are always bound to their
complementary base.Adenine forms two
hydrogen bonds with Thymine, and Cytosine
forms three hydrogen bonds with Guanine.
DNA Double Helix

The strands are wound around each other into a
double helix.
Ribonucleic Acid

RNA is another very important
type of nucleic acid with a
multitude of functions. It stands
for ribonucleic acid.

It is a single stranded molecule,
and has the sugar ribose rather
than the deoxyribose of DNA.

Its bases can temporarily form
hydrogen bonds with
complementary bases.
Types of RNA

RNA is more versatile than DNA, and there are many types
of it that exist. Three main forms it can be found in are
messenger RNA (mRNA), Ribosomal RNA (rRNA), and
Transfer RNA (tRNA).
Differences Between DNA and RNA

DNA and RNA have a few primary
differences in structure:

DNA has deoxyribose and RNA has
ribose

DNA has Thymine and RNA has Uracil

DNA is double stranded and RNA is
single stranded
Nucleoside vs Nucleotide

You may also see
the word
nucleoside, which
refers to the sugar
and the base
without the
phosphate group.
ATP is an example of a nucleoside
triphosphate (adenosine triphosphate).
GTP, UTP and CTP also exist, as does dATP
(deoxyadenosine triphosphate) dGTP, dTTP
and dCTP.
Ubiquity of NTPs

The nucleus, cytoplasm, and organelles of a cell are full
of NTPs and dNTPs. They are used for energy transfer, cell
signalling and can be polymerized into DNA and RNA.
DNA vs Chromatin vs Chromosomes

DNA is found in the nucleus, but it
is entwined with proteins, and
coiled up again and again into a
form called chromatin.

During cell division, chromatin
condenses even further into a form
known as a chromosome, which can
be seen under an optical
microscope.
Crash Course

https://www.youtube.com/watch?v=8kK2zwjRV0M
Review

Define the following terms: nucleotide, complementary
base pairing, phosphodiester bond, NTP.

In a DNA molecule, a purine pairs with a pyrimidine. If this is
the case, then why can’t A-C and G-T pairs form?

The following is a segment taken from a strand of DNA: 5’ATGCCTTA-3’. What would the complementary strand be? Be
sure to include directionality.

A molecule of DNA was analyzed and found to contain 20%
thymine. How much adenine would you expect there to be?
What about the other two bases?

What are the differences between DNA and RNA?

As building DNA is an endergonic process, where do you
expect the energy to come from for the dehydration
synthesis necessary for polymerizing a strand?