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Life Science
5-20-2013
• In Class
– Collect
• Field Trip Permission Slips
– Return Graded Material
• Create Portfolio
– Record Work
– Warm Up
– Introduction to Protein Synthesis
• Homework:
– The Master Molecule of Life
• Crossword Puzzle
How DNA Works
5-17-2013
Name __________________
Warm Up
Unscramble the two words below. Then,
use both of them in one sentence.
tpsoneir
neesg
Complementary Base Pair Answer Key
1. CGTAAGCGCTAATTA
GCATTCGCGATTAAT
2. TCTTAAATGATCGATC
AGAATTTACTAGCTAG
3. AATGAATAGCTAGCTT
TTACTTATCGATCGAA
4. GGCATTCGCGATCATG
CCGTAAGCGCTAGTAC
5. CGTTAGCATGCTTCAT
GCAATCGTACGAAGTA
6. ACTAACGGTAGCTAGC
TGATTGCCATCGATCG
Chapter 7
Section 1 What Does DNA Look Like?
Chapter 7
Section 1 What Does DNA Look Like?
Chapter 7
Section 2 How DNA Works
What You Will Learn
• DNA is bundled with proteins to form
chromosomes.
• DNA stores genetic information in the form of
a code.
• Cells use the DNA code to make proteins.
– Proteins affect traits.
• A mutation is the result of a change in the
genetic code.
Chapter 7
Section 2 How DNA Works
Unraveling DNA
• The total length of DNA in a single
human cell is about 2 m. This is true for
nearly every one of your cells.
• The long molecules fit within the
nucleus because they are wrapped
tightly around proteins. Together, the
DNA and proteins are called
chromosomes.
Chapter 7
Section 2 How DNA Works
Unraveling DNA, continued
• Most of the time, chromosomes exist as
loosely packaged strands called
chromatin.
• Before a cell divides, the chromatin is
bundled into smaller shapes to allow for
mitosis.
Chapter 7
Section 2 How DNA Works
Unraveling DNA, continued
• The unique structure of DNA contains
codes for making proteins.
• The order of bases on a strand of DNA can
code for certain proteins. These codes are
called genes.
• A gene is a string of nucleotides that give
the cell information about how to make a
specific trait.
Chapter 7
Section 2 How DNA Works
As you look at Figure 1 answer the
following questions:
1. Where is the DNA in your cell?
2. How much DNA fits into the nucleus?
3. What is the name for strands of DNA
wound around proteins?
4. When do chromosomes become visible
in cells?
5. What are chromatids?
As you look at Figure 1 answer the
following questions:
1.
2.
3.
4.
Where is the DNA in your cell?
In the nucleus
How much DNA fits into the nucleus?
2 meters
What is the name for strands of DNA wound around proteins?
Chromatin
When do chromosomes become visible in cells?
When the cell is about to divide
5.
What are chromatids?
Two identical copies of a chromosome in a cell that is
about to divide
Chapter 7
Section 2 How DNA Works
Genes and Proteins
• The DNA code is read in a single direction.
Each gene has a starting point and a
stopping point.
• The code works in groups of three. Three
bases code for a single amino acid.
• As the code is read, amino acids are added
in a long chain to form a protein.
Chapter 7
Section 2 How DNA Works
Genes and Proteins, continued
• A typical cell has thousands of genes that
code for thousands of proteins.
• Proteins are responsible for most of the
differences between organisms. Proteins act
as chemical triggers, as messengers, and as
parts of structures.
• Proteins determine the texture of your hair
and the colors you can see, among other
things.
Chapter 7
Section 2 How DNA Works
Genes and Proteins, continued
• RNA, or ribonucleic acid, is another
molecule that helps to make proteins.
RNA serves as a copy of DNA outside
the nucleus.
• RNA copies of DNA genes are made,
then sent to the cytoplasm to code for
proteins.
• RNA is very much like DNA, except it
has the base uracil (U) instead of
thymine.
Chapter 7
Section 2 How DNA Works
Genes and Proteins, continued
• The mirror-like RNA copies are called
messenger RNA (mRNA) because it
carries the message from the DNA.
• mRNA is sent through a ribosome
“protein factory.” Ribosomes are
organelles made of RNA and protein.
Chapter 7
Section 2 How DNA Works
Genes and Proteins, continued
• The mRNA code is read by transfer RNA
(tRNA). The transfer RNA carries specific
amino acids from the cytoplasm.
• The bases of tRNA fit into the bases of
mRNA, ensuring that the proper amino
acids are put into place.
• The growing chain of amino acids folds into
a protein molecule.
Chapter 7
Section 2 How DNA Works
Chapter 7
Section 2 How DNA Works
Chapter 7
Section 2 How DNA Works
Changes in Genes
• Like a change in the letters of a
sentence, a change in the sequence of
bases in DNA can change the meaning
of the code.
• A change in the nucleotide-base
sequence of DNA is called a mutation.
• Mutations occur due to errors during
Chapter 7
Section 2 How DNA Works
Changes in Genes, continued
• Changes in DNA may cause no change
in a trait, or it may cause a harmful trait
or an improved trait.
• Some mutations do not change the
protein that a gene codes for, so there is
no effect.
• A mutation that improves a trait makes
Chapter 7
Section 2 How DNA Works
Changes in Genes, continued
• Mutations are rarely helpful, so cells
make proteins that detect and repair
mutations.
• If a mutation occurs in a sex cell (egg or
sperm) it can be passed on to offspring.