Download Unit 1 – Notes #2 DNA Structure - Mr. Lesiuk

Unit 1 – Notes #2 DNA Structure
Cellular Chemicals :
- All life forms are composed of at least one cell,
anything smaller than a cell unit does not
have life.
- A cell has all the equipment (organelles)
needed to sustain life, provided that it is
supplied with the correct chemicals.
-
What is so unusual, is that living things are
made up of non-living chemicals.
- These chemicals can react with oxygen to
release energy for the cell while other
chemicals can be used as building materials
for growth and repair.
- Many of these chemicals fit into three major
nutrient groups:
1. Carbohydrates
Ex. Sugars and starch
2. Lipids
Ex. Oil and butter
3. Proteins
Ex. Meat and cheese
Proteins :
- Unlike the first two groups, proteins are
primarily used for building the structural
components of a cell rather than providing
energy for a cell.
- After protein molecules are ingested by an
animal they are broken down into their tiny
building blocks (20 different amino acids),
these AA’s are then transported to the
organisms cells.
-
- The cell uses these amino acids to build new
proteins for cells to grow and repair
themselves as well as to make new cells
through cell division (mitosis).
- The blue-prints and processes for building
these proteins are quite intricate, and the
control of protein synthesis is governed by the
nucleus of the cell.
- If you think of a cell as being like a town, the
nucleus would be like “City Hall”.
- Cells make a wide variety of proteins, by
stringing these different AA’s into almost
endless ways. Much like we can make a
variety of words from just 26 letters of the
alphabet.
- Each type of protein plays an important role
in cellular activity and each protein must be
built correctly to function properly.
- The blue-prints (genes) for these various
proteins are found in the nucleus of the cell.
These varying genes are found strung
together on extremely long strands of DNA.
DNA : Deoxyribonucleic Acid
- Almost all body cells contain the full amount of
DNA in their nucleus, so that they have the
adequate amount of DNA to make other cells.
Exceptions:
1. Red Blood Cells do not have a nucleus when
mature.
2. Sex Cells (Sperm and Egg) only have ½ the
amount of DNA of a normal cell.
- The DNA molecule is the only molecule known
that is capable of duplicating (replicating) itself.
- Most of the time, the DNA is found in the form
of a long String called Chromatin.
- During cell division (mitosis), Chromatin
bunches up to form Chromosomes.
- Humans have 46 chromosomes in each cell,
but only 23 chromosomes in the sex cells.
- A section of a chromosome, which codes for a
certain protein, is called a gene.
DNA Structure :
- All DNA, regardless of the type of organism,
is composed of units called nucleotides, each
nucleotide consists of the following 3 types of
molecules:
A) a 5 carbon sugar called deoxyribose.
B) a phosphate group.
C) and one of four types of nitrogenous bases.
- These 3 molecules link together result in a
nucleotide.
NUCLEOTIDES join together
to form Nucleic Acids like
DNA
- There are 2 different categories of bases that
stick off of the sugar part of the nucleotide:
1) Purines: (Adenine and Guanine)
-larger
-have 2 fused rings
2) Pyrimidines(Thymine and Cytosine)
- shorter
- have only one ring
- When the bases bond together to form the
“rungs of the DNA ladder they do so in a set
pattern. The alternating sugar and phosphates
make up the rails (backbone). The bases make up
the rungs.
- One Purine (an A or G) base always joins
with one Pyrimidine (a C or T) base. This
bonding of bases is called Complementary
Base Pairing.
- Complementary Base Pairing is even more
specific, because Adenine always bonds to
Thymine, and Guanine always bonds to Cytosine.
A=T
G=C
-If 2 purines bonded together they would be too
long and they would overlap, and if 2 pyrimidines
bonded together they would be too short.
- Weak Hydrogen bonds hold the 2
complementary bases together at the center of the
DNA molecule.
- The complimentary strands link together to form
a ladder, the ladder then twists to form what looks
like a winding spiral staircase this is called a
double helix.