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.