1. What is DNA?
Ms. Alvarado
Living Earth
9th grade
DNA, RNA, AND PROTEIN SYNTHESIS
2. Recall from last class
● HS-LS1-1. Construct an explanation
based on evidence for how the
structure of DNA determines the
structure of proteins, which carry out
the essential functions of life through
systems of specialized cells
● Students will use vocabulary terms to
describe the structure of DNA and the
functions carried out
● Students will be able to recall the basic
structure of DNA, including the
complementary base pairings,
Learning goals
● Modern cell theory: cells are
the basic structural,
functional, and organizational
units of both single-celled
and multicellular organisms;
cells divide and pass on
hereditary information; and
energy flows within cells.
3. What do you know about your DNA?
Let’s do a quick activity on how well
you know yourself and how much
you know about humans. In your
composition books, write down a
“recipe” for what it takes to make a
human or what it takes to make
yourself. You can start with a list of
big and small factors to get your
ideas down in your notebooks. You
have five minutes to work with your
groups.
Big Small
4. What is DNA?
We know that the basic unit of all living organisms, from bacteria to humans, is
the cell. Contained within the nucleus of these cells is a molecule called DNA.
Today we know that DNA is the blueprint used to build an organism-our genetic
makeup, or genotype, controls our phenotype. The directions coded for by our
genes controls everything from growth and development to cell specification and
metabolism (the process by which the body changes food and drink into energy)
● DNA= Deoxyribonucelic acid
● genotype: the complete set of genetic material; a person’s unique sequence
of DNA
● phenotype: the observable characteristics of the individual’s genetic material
(what you can see)
5. What can DNA tell us?
● Genetic ancestry testing- Examination of DNA variations can provide
clues about where a person's ancestors might have come from and
about relationships between families
○ Can confirm if you have or don’t have a specific disease
● Forensic science- The most common sampling method is cheek
swabs. However, science has progressed to the point that DNA
samples can be collected from a variety of techniques and materials.
So, you can collect DNA from bones, teeth, cigarette butts, and most
other biological matter.
6. What can DNA tell us?
● Paternity testing- You never know when paternity testing is
going to be necessary. In cases such as custody hearings and
child support battles, the paternity and maternity of a child are
of the utmost importance. So, by testing the DNA of the child
and the parents, you can have definitive proof of the parentage.
7.
8. How did we get to know so much about it?
The Swiss physician Friedrich Miescher
discovered DNA in 1868, when he
purified a novel substance from the
nucleus of white blood cells. This
molecule, which he called “nuclein”, had
chemical properties unlike any substance
previously identified. By the end of the
19th century, scientists described DNA as
a polymer composed of building blocks
known as nucleotides (this should seem
familiar!)
Week 12: Biomolecules
● All living things on Earth contain
carbon, and these compounds
are called organic compounds.
There are 4 important organic
compounds: lipids, carbs,
proteins, and nucleic acids
● Which type of biomolecule is
DNA?
9. What is the structure of DNA?
A strand of DNA is composed of building blocks known as nucleotides. Each
nucleotide is composed of 3 basic parts:
1. phosphate group
2. deoxyribose sugar
3. nitrogen-containing base (adenine, cytosine, guanine, thymine) or (A, C, G,
T)
The sugar of one nucleotide forms a
covalent bond with the phosphate group of
its neighbor, making DNA a stable structure
for genetic information. The order of these
nucleotides gives rise to genes, each with a
unique sequence.
10.
11. The discovery of DNA’s structure
● In 1953, James Watson and Francis Crick
determined that DNA forms a double helix
structure, similar to a ladder that spirals
around a central axis.
● The discovery of the structure of DNA in 1953
was made possible by Dr Rosalind Franklin’s
X-ray diffraction work at King’s. Her creation
of the famous Photo 51 demonstrated the
double-helix structure of deoxyribonucleic
acid: the molecule containing the genetic
instructions for the development of all living
organisms.
12. What is the structure of DNA?
● The rungs of the ladder are formed by hydrogen
bonds between bases.
● Base Pairs
○ The nitrogen bases bond together in a specific
way.
■ Adenine only bonds to Thymine
A—T
■ Guanine only bonds to Cytosine
G—C
○ This principle is known as complementary base
pairing.
■ The bases connect to each other through
hydrogen bonds
13. Nitrogenous bases
Purines and pyrimidines are the two families of nitrogenous bases that make up
nucleic acids. Each DNA strand has a ‘backbone’ that is made up of a sugar-
phosphate chain. Attached to each one of these sugars is a nitrogenous base
that is composed of carbon and nitrogen rings. The number of rings this base
has determines whether the base is a purine (two rings) or a pyrimidine (one
ring).
14. Nitrogenous bases
There are 2 main types of purine:
1. Adenine
2. Guanine
There are 2 main types of pyrimidines:
1. Thymine
2. Cytosine
17. Quick break
With the person next to you, write down 2 noticings and 1
wondering about the the diagram of the DNA ladder I just
showed you. Is there anything missing? Is the direction of the
DNA strands correct? Jot down these notes in your
composition books.
18. DNA’s antiparallel structure
● DNA is composed of two strands of
nucleotides.
● The two DNA strands are antiparallel.
○ antiparallel= opposite directions
● One strand runs 5′ to 3′, and the
other strand runs 3′ to 5′.
● The two DNA strands wind around
each other, forming a double helix.
19.
20. DNA construction ladder
1. Start off by gluing the left DNA backbone strands on each
other in a row (3 of them)
2. Glue the phosphates on the DNA backbone
3. Right above the phosphate glue the sugar base
4. Glue the bases (A, T, C, G) next to the sugar
5. The left DNA strand and sugars/bases points up, the right
DNA strand is opposite and the sugars/bases point down
To add to this activity, where do these come from?
The purines on one strand of DNA form hydrogen bonds with the corresponding pyrimidines on the opposite strand of DNA, and vice versa, to hold the two strands together. Within DNA molecules, this is their most important function and is known as base pairing. Because purines always bind with pyrimidines – known as complementary pairing – the ratio of the two will always be constant within a DNA molecule. In other words, one strand of DNA will always be an exact complement of the other as far as purines and pyrimidines go.
https://www.albert.io/blog/what-is-the-difference-between-purines-and-pyrimidines/
The purines on one strand of DNA form hydrogen bonds with the corresponding pyrimidines on the opposite strand of DNA, and vice versa, to hold the two strands together. Within DNA molecules, this is their most important function and is known as base pairing. Because purines always bind with pyrimidines – known as complementary pairing – the ratio of the two will always be constant within a DNA molecule. In other words, one strand of DNA will always be an exact complement of the other as far as purines and pyrimidines go.
https://www.albert.io/blog/what-is-the-difference-between-purines-and-pyrimidines/
