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Structure and Function of DNA
1. DNA stands for
deoxyribonucleic acid.
2. Watson and Crick were the first scientists to construct a working model of DNA in 1953.
3. DNA is found in the nucleus of the cell.
4. Genetic material of living things is made of DNA.
5. Composed of 2 strands, or chains. (double-stranded)
6. Double helix shape (twisted, coiled)
7. DNA is a very long molecule that is made up of smaller subunits called nucleotides which consist of three parts:
a. Simple sugar (sugar in
DNA is deoxyribose)
b. Phosphate group
c. Nitrogen base
8. DNA contains four nitrogen bases:
a. Adenine (A) A-T
b. Thymine (T)
c. Cytosine (C) C-G
d. Guanine (G)
9. Adenine and Guanine are double-ring bases called purines. (HINT: purines have nine sides and hence are noted by adenine and guanine)
Adenine
Guanine
10. Cytosine and Thymine are smaller, single-ring bases called pyrimidines. (HINT: pYrimidines (cytosine and thymine) contain the letter Y)
Cytosine
Thymine
11. The two chains of
nucleotides are joined by
hydrogen bonds.
12.Sides of DNA are made
up of a sugar and phosphate.
13. In each chain of nucleotides, sugar of one nucleotide is joined to the phosphate group of the next nucleotide by a covalent bond.
14.Rungs of DNA are the nitrogen base pairs.15. Base pair – 2 bases on the
same rung16. In DNA, cytosine always
bonds with guanine and adenine always bonds with thymine.
17.Organisms are different from each other, even though their genetic material is made up of the same molecules, because the order of nucleotides in their DNA is different.
DNA: Double Helix WS
Notes:
1. Building block is the nucleotide:
Phosphate group
5-C sugar deoxyribose
nitrogen base
1. Adenine (A)
2. Thymine (T)
3. Cytosine (C)
4. Guanine (G)
2. Double helix structure held together by weak hydrogen bonds.
3. Which nitrogen bases always pair?
cytosine with guanine
adenine with thymine
Genes determine your traits or characteristics. (At least one gene per trait.)
How many chromosomes in humans? 46
How many genes? Thousands (100,000)
A chromosome is just one long strand of a DNA molecule.
Answers to picture:1. Cell(cytoplasm)2. Nucleus3. Chromosome4. Gene
DNA and Genes WorksheetStudy the Diagram:When the DNA ladder replicates, or
copies itself, the ladder breaks apart. You can think of the ladder breaking a part as a zipper unzipping. When the two sides of the ladder are apart, free nucleotides attach to the nucleotides already on the sides of the ladder, and two
copies of the DNA are formed. The copies are the same as the original because adenine (A) usually pairs with thymine (T). Cytosine (C) usually pairs with guanine (G).The diagram below shows an unzipped strand of DNA. Write the letters (A,T,C, or G) of the bases that will pair with the bases on the strand. Some of the bases have been paired for you.
C-GT-AA-TG-CG-CT-AC-GA-TA-TT-A
1. True or False? Nucleotide bases already attached to proteins form the copied side of the DNA ladder. False
2. True or False? The process of DNA replication results in a copy of the original strand of DNA. True
3. True or False? Sugar and phosphates provide the energy for DNA replication. False
4. True or False? The final result of DNA replication is two copies of the original DNA strand. True
DNA Replication
1. Replication is the process by which DNA copies itself before mitosis or meiosis, so that each daughter cell will have an exact copy of the genetic code.
2. Occurs in the nucleus.
3. Steps of replication:
a. Two strands of DNA separate at their base pairs by breaking, or unzipping, the hydrogen bonds.
b. Each strand builds its opposite strand by base pairing with free-floating nucleotides. Each guanine (G) pairs with cytosine (C), while each thymine (T) pairs with an adenine (A).
c. Each original strand
serves as a template or
pattern for the creation
of a new strand.
d. Each new DNA molecule will have one strand of nucleotides from the original, or parent, strand and one strand of nucleotides from the free-floating nucleotides.
e. Results in the formation of two DNA molecules each of which is identical to the original DNA molecule.
4. Draw the newly formed strands on this “unzipped” DNA molecule to show replication occurring:
Original New New Original A----------T A----------T T----------A T---------A C----------G C---------G G----------C G---------C C----------G C---------G A----------T A---------T T----------A T---------A
DNA Code1. The message of the DNA
code is information for building proteins.
2. Proteins become important structures, such as filaments in muscle tissue,
walls of blood vessels, and transport proteins in membranes.
3. Other proteins, such as enzymes, control all the chemical reactions of an organism.
4. Proteins are built from chains of amino acids.
5. A codon is a set of three nitrogen bases representing an amino acid.
a. 64 are in the genetic
code.
b. 61 code for amino acids. c. 3 are stop signals (terminator codons) for the chain synthesis. (Terminator codons do not code for an amino acid)
d. More than one codon can code for the same amino acid; however, for any one codon, there is only one amino acid.
6. The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein.
7. It is estimated that each human cell contains about 80,000 genes.
8. Genetic code is universal because the codons represent the same amino acids in all organisms.
RNA9. RNA stands for ribonucleic
acid.
10.Single-stranded
11.Contains the sugar, ribose
12. Contains four nitrogen bases: a. Adenine (A) A-U b. Uracil (U)** **Uracil takes the place of
thymine in RNA c. Cytosine (C) C-G d. Guanine (G)
13. Three types of RNA:
a. mRNA (messenger RNA) – brings information from the DNA in the nucleus to the cell’s factory floor, the cytoplasm
b. tRNA (transfer RNA) – transports amino acids to the ribosomes for protein synthesis
c. rRNA (ribosomal RNA)– makes up the ribosomes
Transcription of DNA1. Occurs in the nucleus.2. Transcription – process of
making RNA from DNA3. Begins as enzymes unzip
the DNA molecule. (This results in only one single-stranded RNA molecule.)
4. Free RNA nucleotides (with uracil) pair with complementary bases on one unzipped strand of DNA. (**Uracil(U) pairs with adenine(A), cytosine(C) pairs with guanine(G), & thymine(T) pairs with adenine(A).
5. When base pairing is completed, mRNA leaves the nucleus and enters the cytoplasm.
6. Suppose the following strand from a segment of DNA is being copied during transcription to make mRNA. Complete the structure for mRNA before it unattaches from the DNA strand.
DNA mRNA A----------U T----------A G----------C G----------C C----------G A----------U G----------C T----------A C----------G
Difference between DNA & RNA
Translation: From mRNA to Protein
1. Translation-process in which DNA’s code is translated from mRNA into a sequence of amino acids that make up protein.
2. Occurs at the ribosomes in the cytoplasm.
3. Begins as the first codon of mRNA attaches to a ribosome. (AUG is the start codon which signals the start of protein synthesis-codes for the amino acid methionine)
4. tRNA brings amino acids to the ribosomes.
5. tRNA’s anticodon pairs with mRNA’s codons
Ex. mRNA strand: AUG
tRNA strand: UAC
6. Amino acids bond together to form a protein. A peptide bond joins these amino acids.
7. As translation continues, a chain of amino acids is formed until the ribosome reaches a stop codon on the mRNA strand. At this point,
a protein is formed, and the mRNA falls off the ribosome to the cytoplasm.
8. What amino acid is coded for by the mRNA base pair sequence? (see the mRNA code)
a. C-C-C proline
b. A-A-A lysine
c. G-C-U alanine
d. A-G-U serine
e. U-U-A leucine
f. C-A-C histidine
9. Identify the amino acid sequence coded for by this short strand of mRNA:
A-U-G U-U-C U-C-G G-U-U met phe ser valA-A-A G-G-G U-G-A lys gly stop
SUMMARY REVIEW:10. Which molecule contains
the genetic code for making all proteins in your body? DNA
11. Which type of RNA has the code for making a specific protein? mRNA
12. Which type of RNA picks up the amino acids in the cytoplasm from the digestion of foods and delivers them to the ribosomes for assembly into proteins? tRNA
CODON CHART
Chemical Basis of Genetics (Translation) Worksheet
The sequence of bases of a DNA molecule directs the formation of proteins. Genes usually make either a single protein or a polypeptide, a sequence of amino acids that make up a large part of the protein molecule.
Study the diagrams below. On the right is the genetic code, showing the codons for each amino acid. On the left is the sequence of bases in the gene that makes beef insulin, a protein that breaks down sugar in cow’s blood. Use these two
Diagrams to fill in the correct sequence of amino acids in the beef insulin molecule shown below.
1. UUU phe
2. GUC val
3. AAU asn
4. CAG gln
5. CAU his
6. CUG leu
7. UGU cys
8. GGG gly
9. AGU ser
10.CAC his
11.CUA leu
12.GUC val
13.CAG gln
14.GCC ala
15.CUA leu
16.UAU tyr
17.UUG leu
18.GUU val
19.UGC cys
20.GGC gly
21.GAG glu
22.AGA arg
23.GGG gly
24.UUC phe
25.UUU phe
26.UAC tyr
27.UAC tyr
28.CCC pro
29.AAA lys
30.GCA ala
31.GGU gly
32.AUU ile
33.GUG val
34.GAA glu
35.CAG gln
36.UGU cys
37.UGU cys
38.CGU arg
39.UCU ser
40.GUU val
41.UGU cys
42.UCG ser
43.UUG leu
44.UAC tyr
45.CAA gln
46.UUG leu
47.GAG glu
48.AAU asn
49.UAU tyr
50.UGU cys
51.AAC asn
52.UAG term (stop codon)
Protein Synthesis WS
1. mRNA is made from one strand of DNA.
2. mRNA is made in the nucleus of cells.
3. After mRNA is made, it leaves the nucleus through nuclear pores and goes to a ribosome in the cytoplasm.
4. Ribosomes are the site of protein synthesis.
RNA Transcription:5. An enzyme called RNA
polymerase unzips DNA so that one strand of DNA serves as a pattern.
6. mRNA will “read” DNA’s code for protein synthesis.
7. This occurs when mRNA nucleotides attach to complementary bases on DNA’s strand.
8. Example:
DNA: TAC CTA AAC CCA
mRNA:AUG GAU UUG GGU
DNA: TCT CAT TGA
mRNA: AGA GUA ACU
RNA Translation:
9. In a process called translation, DNA’s code on making proteins will be translated from mRNA to amino acids.
10. mRNA is attached to ribosomes in the cytoplasm.
11. tRNA anticodons will attach to mRNA’s codons.
12. tRNA is bringing amino acids to the ribosome.
13. When 20 amino acids bond together, a protein is made.
14. Peptide bonds hold the amino acids together.
15. Example:
DNA: TAC CTA AAC CCA
mRNA:AUG GAU UUG GGU
Amino: met asp leu gly
acid
tRNA:UAC CUA AAC CCA
DNA: TCT CAT TGA
mRNA: AGA GUA ACU
Amino: arg val thr
acid
tRNA: UCU CAU UGA
Mutation: Genetic Changes Notes
I. Mutation – any change in the DNA sequence that also changes the protein it codes for
A. A wrong base in DNA gives the cell the wrong message; the result is the wrong type of protein is made
and the change may cause different traits to appear.
B. Occurs in the nucleus of the cell during the replication process of cell division. (during mitosis or meiosis)
C. Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a gene in a sperm or egg cell. If these cells take part in fertilization, the altered gene would become part of the genetic makeup of the offspring. (meiosis)
D. Mutations can affect the body cells (ex. skin, muscle, bone). If the cell’s DNA is changed, this mutation would not be passed on to offspring. However, the mutation may cause problems for the individual. (mitosis)
II. Two major groups of mutations:
A. Gene mutation-involves individual genes on a chromosome
B. Chromosomal mutation-involves whole chromosomes
III. Gene mutations-involve a single nucleotide or affect sections of DNA that include many nucleotides
A. Point mutation-a change in a single base pair in DNA; these are less harmful to an organism because they disrupt only a single codon
EX. Normal
mRNA: AUG AAG UUU GGC
Protein: met lys phe gly
mRNA: GCA UUG UAA
Protein: ala leu stop
Point Mutation
mRNA: AUG AAG UUU AGC
Protein: met lys phe ser
mRNA: GCA UUG UAA
Protein: ala leu stop
Example: Sickle-cell anemia: Substitution of a single base in the gene for hemoglobin can produce the gene for sickle-cell hemoglobin
B. Frameshift mutation-where a single nitrogen base is added or deleted from DNA
1. Addition or deletion causes the genetic code to be read out of sequence.
2. Every codon (and amino acid) after the addition or deletion is changed or different.
Normal
mRNA: AUG AAG UUU* GGC
Protein: met lys phe gly
mRNA: GCA UUG UAA
Protein: ala leu stop
Frameshift Mutation
mRNA: AUG AAG UUG GCG
Protein: met lys leu ala
mRNA: CAU UGU AA……
Protein: his cys……….
IV. Chromosomal Mutations-where parts of the chromosome are broken off and lost during mitosis or meiosis
A. Many chromosomal mutations result from the failure of chromosomes to separate properly during meiosis.
Nondisjunction is the failure of homologous chromosomes to separate properly during meiosis. (Note: During Meiosis I, 1 chromosome from each homologous pair moves to each pole of the cell; occasionally, error occurs in which both chromosomes of a homologous pair move to the same pole.
Effects of nondisjunction are often seen when gametes fuse in fertilization – 1 gamete has an extra chromosome, 1 gamete is missing a chromosome)
E. Types of chromosomal mutations:
Deletion-occurs when part of a chromosome is left out (most are lethal)
Inversion-occurs when part of a chromosome breaks off and is reinserted backwards.
Insertion-occurs when a part of a chromatid breaks off and attaches to its sister chromatid. The result is a duplication of genes on the same chromosome.
Translocation-occurs when part of one chromosome breaks off and is added to a different chromosome. (changes the number)
Chromosomal mutations may be serious because they affect the distribution of genes to the gametes during meiosis.
Few chromosomal mutations are passed on to the next generation because the zygote usually dies.
In cases where the zygote develops, the mature organism is sterile and incapable of producing offspring.
V. Causes of Mutations:
A. Usually occur at random (these are called spontaneous mutations).
B. Many are caused by factors in the environment. Any agent that can cause a change in DNA is called a mutagen.
***Mutagens include: high energy radiation, chemicals, & even high temperatures; forms of radiation, such as X-rays, cosmic rays, UV light, & nuclear radiation; chemical mutagens include dioxides, asbestos, benzene, cyanide, & formaldehyde
C. Errors in DNA provide variation that enable species to evolve.
D. Mutations result in sterility or the lack of development in an organism.
E. If mutations occur in human gametes (called germ cell mutations), they can cause birth defects.
F. If mutations occur in body cells (called somatic mutations), they can lead to cancer.
1. Oncogene-gene hat causes a cell to become cancerous.
2. Causes of cancer: a. Some are inherited. b. Some result from
environmental factors. c. Some are a combination of
genetic & environmental factors.