Structure and Function
Dec 22, 2015
What do the letters DNA stand for?◦ Deoxyribonucleic acid
Where is DNA located? ◦ Prokaryotic cells: in the cytoplasm◦ Eukaryotic cells : in the nucleus
How many pieces of DNA are in cells?◦ Prokaryotic cells: one, circular piece of DNA◦ Eukaryotic cells: several, linear pieces of
DNA (46 in humans)
1) chromosome: ◦ tightly packed strands of DNA found in
a dividing cell. ◦ Usually shown as a doubled
chromosome, or X-shape
You have __46______ chromosomes in your body cells.
Each piece is about __5______ cm long. What is the total length of DNA in one body
cell? 3_ meters! (9 ft)
How does that much DNA fit inside each of your cells?◦ Tied around histones
Histones are proteins which act like thread spools. DNA is wound around the histones in order to fit inside a cell.
Why have 2 different forms of DNA in your cells?◦ The advantage of chromosomes is
_condensed genetic material can easily be moved to new cells during cell division.
◦ The advantage of chromatin is __loose genetic material can be ‘read’ because the DNA code is exposed.
Each one of your body cells has an exact copy of DNA.
That includes toe cells and nose cells, ear cells and eye cells!
Every species of eukaryotic organisms have a specific number of chromosomes in each cell: Organism Number of
Chromosomes in each cell.
Why are these numbers so different?
goldfish 94
chicken 78
horse 64 1) ____chromosomes come in different sizes__
sand dollar 52
chimpanzee 48 2) __different organisms have different numbers of genes_
dog 48
human 46
brown bat 44
corn plant 20
housefly 12
fruit fly 8
Gene: 1) A unit of hereditary information which can
be passed on to future generations. 2) A segment of DNA on a chromosome
which holds the code or ‘recipe’ for a protein.
3) Genes hold the code for synthesis of ◦ proteins : a functional group of many amino
acids
◦ Polypeptides: a smaller, non-functional group of amino acids (part of a protein)
◦ traits or parts of a trait : physical, behavioral and physiological traits
Review of the amino acid structure of proteins: Circle the R groups to identify individual aa’s.
How many different KINDS OF amino acids could be used to form a single protein or polypeptide? __20, one for each R group
Which group of organic compounds does DNA belong to? nucleic acids
Considering that DNA is a long molecule that must periodically be copied, it must be composed of simple units that fit together easily.
DNA is made of repeating subunits called nucleotides. Each nucleotide is made up of 3 parts:
◦ a)_sugar______________◦ b) __phosphate group (PO4)◦ c) _nitrogen base_____
The sugar, __deoxyribose__and the phosphate groups are identical in all DNA nucleotides but there are four different types of nitrogen bases:◦ __adenine (A)_________________ ◦ __guanine (G)________________ ◦ __thymine (T)_______________◦ ___cytosine (C)______________
3) One of four different nitrogen bases:
PURINES◦ Adenine:
◦ Guanine:
PYRIMIDINES◦ Thymine:
◦ Cytosine:
As you can see, the chemical structure of a nucleotide is difficult to draw so we normally draw a nucleotide using symbols/letters to represent the parts.
In the diagram above, what does the "A" stand for?____adenine___
What other letters could be used in that position? T, C, G
In the diagram above, what does the "S" stand for?_sugar_
In the diagram above, what does the "P" stand for? phosphate group
How many different types of nitrogen bases are
there in DNA? ___4________
Name them:___adenine, thymine, guanine, cytosine_
If each nucleotide contains _one__ nitrogen base. How many different types of DNA nucleotides can
be formed? _four
NOTE: Another type of nucleotide, Uracil, will replace the Thymine nucleotide in RNA molecules.
The drawing below is a MODEL representing a short piece of a DNA molecule. The key identifies phosphates, sugar and nitrogen bases.
The bonds that hold the molecules together in DNA are strong, covalent bonds.
The bonds holding the nitrogen bases are NOT covalent but are weak, hydrogen bonds.
What does each nucleotide have in common? ___sugar, PO4__
How do nucleotides differ from each other? ____different nitrogen base_
Notice that each nucleotide bonds with a nucleotide above and below it. This forms a strand of DNA.
How many strands make up a molecule of DNA? 2
The two strands are then twisted into a spiral shape, double stranded structure called a double helix.
Look at the model of DNA on the previous page. Use a red, blue, yellow and green colored pencil and follow the directions to answer the questions:
Look at drawing A. Circle a nucleotide on the right hand side or strand of the DNA molecule. What three parts can you identify?
1. ___sugar 2. __phosphate (PO4) 3. __nitrogen base__
List the names of the different bases: __A= adenine, G= guanine, C= cytosine, T= thymine__ Color the circled nucleotide. Color sugar red and the phosphate blue.
What is the name of the nitrogen base that you have circled?
Color the bases as follows: adenine and guanine-yellow, cytosine and thymine-green.
Circle another nucleotide on the left hand strand of the DNA molecule. Color the sugar, phosphorous and nitrogen base as above.
Imagine that the molecule of DNA in drawing A looks like a ladder. What two molecules make up the sides of the ladder? ___sugar__ and ___phosphate group
What two molecules make up the rungs of the ladder? (Rungs are where you place your feet.) ____one nitrogen base_ and a second, complimentary nitrogen base_
Color the remainder of the DNA molecule in drawing A according to the directions.
At what point are the right and left strands of DNA nucleotides joined?_between nitrogen bases
Is there any order to the pairing of the nitrogen bases down the center of the DNA molecule?◦ adenine is hydrogen bonded to thymine◦ cytosine is hydrogen bonded to guanine
Is this a pairing of purines with pyrimidines? ___purine is bonded with pyrimidine_______
Is there any order to the nucleotides down the right hand strand of the DNA molecule?
__no__ Is there any order to the nucleotides down
the left hand strand of the molecule? ___no____
In a molecule of DNA, adenine is always paired with __thymine T___
In a molecule of DNA, guanine is always paired with ___cytosine C_
In a molecule of DNA, a purine is always paired with a ___pyrimidine
We call this system of base pairing __complimentary base pairing___
If the sequence of nucleotides in one strand of a DNA molecule is
T-A-C-G-G-T-C-A-A What would be the complementary base pairs on the other strand?
A-T-G-C-C-A-G-T-T Describe the shape of the DNA molecule in drawing B. twisted
ladder We call this twisted, double strand shape a ___double helix___
A segment of DNA is composed of 100 base pairs. If 25 of the nitrogen bases are adenine, how many are thymine?
a. 15 b. 20 c. 25 d. 30 e. 35
Human DNA contains about 10% cytosine. What percent of the bases are thymine?
a. 10% b. 20% c. 40% d. 80% e. 90%
Chromosomes can be seen in a single or double-arm, replicated form
Two configurations of chromosomes:
1) Single arm chromosomes are composed of a single chromatid.
2) Double-arm chromosomes are
made up of paired, genetically identical chromati called sister chromatids. Sister chromatids are joined at the centromere. Because sister chromatids are formed during replication of DNA, they are identical right down to the nucleotide sequences!
Complete the blanks showing the "central dogma" of molecular biology.
DNA --> _____________ --> ______________ --> _______________
What process is illustrated by the arrow below?
A: DNA duplication B: DNA diploidy C: DNA replication D: DNA mutation
James Watson and Frances Crick (1953):along with Maurice Wilkins, were awarded the Nobel Prize for determining the structure of DNA.
Rosalind Franklin (1951):Expert in X-ray Crystallography, her work was used by Watson to determine the structure. Died before the prize was given out—cannot be awarded posthumously.
Genome :The entire set of genes that make up the DNA of an organism.
Completed in 2003, the Human Genome Project (HGP) was a 13-year
project coordinated by the U.S. Department of Energy and the National Institutes of Health. During the early years of the HGP, the Welcome Trust (U.K.) became a major partner; additional contributions came from Japan, France, Germany, China, and others. Project goals were to:
identify all the approximately 20,000-25,000 genes in human DNA, determine the sequences of the 3 billion chemical base pairs that
make up human DNA, store this information in databases, improve tools for data analysis, transfer related technologies to the private sector, and address the ethical, legal, and social issues (ELSI) that may arise
from the project. (Source: http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml)
DNA unwinds and unzips from the enzyme DNA helicase.
DNA polymerase helps to link free floating DNA nucleotides between complimentary nucleotides.
Covalent Bonds Join nucleotides on the SAME strand and Hydrogen Bonds between opposite strands.
Each new DNA strand formed contains the SAME sequence of nucleotides.