DNA and Its Functions

3.1 DNA Structure

Double-stranded helical polymer of nucleotides, held together by H-bond between bases

A, T, G, C

Deoxyribose and phosphate group

Within any DNA molecule, the amount of thymine is always equal to the amount of adenine (same for GC)

These are called complementary pairs

REPLICATIONPROTEIN SYNTHESIS

MUTATIONSRECOMBINANT DNA

Functions of DNA

3.2 Replication

The replication of DNA is required in order for cells to divide

Replication occurs during Interphase of mitosis

Three steps

The enzyme, DNA helicase breaks the H-bonds causing it to unzip, exposing the bonding locations of their bases

New DNA nucleotides move into the nucleus where DNA polymerase enzymes ensure they bond onto their exposed complementary bases on the parent strands

The Process continues along the length of the parent strands and results in two separate identical DNA molecules each with an original strand and a new strand.

Review

Equal amount of A and T in DNA is logical because

a) These molecules bond together

b) DNA is a double stranded helix

c) These molecules are not the same size

d) One is a purine and one is a pyrimidine

Equal amount of A and T in DNA is logical because

a) These molecules bond together

b) DNA is a double stranded helix

c) These molecules are not the same size

d) One is a purine and one is a pyrimidine

DNA molecules from unrelated organisms differ in their

a) Types of sugar

b) Number of strands

c) Sequence of bases

d) Order of phosphates

DNA molecules from unrelated organisms differ in their

a) Types of sugar

b) Number of strands

c) Sequence of bases

d) Order of phosphates

Replication MOST accurately refers to the synthesis of

a) Complementary strands of RNA for mitosis

b) Complementary strands of DNA for mitosis

c) Proteins based on the sequence of bases in RNA

d) Proteins based on the sequence of bases in DNA

Replication MOST accurately refers to the synthesis of

a) Complementary strands of RNA for mitosis

b) Complementary strands of DNA for mitosis

c) Proteins based on the sequence of bases in RNA

d) Proteins based on the sequence of bases in DNA

A polymer of nucleic acid is found in the cytoplasm of a living animal cell. Which of the following is MOST likely true about this molecule?

a) Helicalb) Contains ribosec) Double strandedd) Contains thymine

A polymer of nucleic acid is found in the cytoplasm of a living animal cell. Which of the following is MOST likely true about this molecule?

a) Helicalb) Contains ribosec) Double strandedd) Contains thymine

Which of the following is true for any given strand of DNA?

a) [A] = [C], [T] = [G]

b) [A] = [G], [T] = [C]

c) [A] + [T] = [G] + [C]

d) [A] + [G] = [T] + [C]

Which of the following is true for any given strand of DNA?

a) [A] = [C], [T] = [G]

b) [A] = [G], [T] = [C]

c) [A] + [T] = [G] + [C]

d) [A] + [G] = [T] + [C]

3.3 Protein Synthesis

Another function of DNA is the assembly of amino acids into proteins at the ribosomes

The ribosomes can either be

embedded in the walls of the RER, usually following the secretory pathway and are exported via exocytosis

located free In the cytoplasm if it is to be used within the cell

A gene functions to directly make messenger RNA (mRNA)

To start, the DNA in the region of the gene “puffs up” by breaking the H-bonds between base pairs

The beginning point for thesynthesis of mRNA is marked by the sequence of nucleotide TAC (bases) on DNA

This process is calledtranscription

Once constructed, mRNA leaves the nucleus and becomes associated with a ribosome where the protein will actually be formed

Each set of 3 nucleotides from an mRNA strand functions as a codon, which gives 64 different combinations

These triplets determine which of the 20 amino acids is to be delivered to the ribosome

Translation is the second phase of protein synthesis and it occurs at the ribosomes

mRNA arrives at ribomose where ribosomal RNA (rRNA) helps align it into the correct position on the ribosome with AUG (methionine) as the start codon for building a protein

Transfer RNA (tRNA) molecules, with anticodons complementary to the mRNA codons, transport specific amino acids into place at the ribosomes

Incoming amino acids are linked by the formation of peptide bonds to the growing polypeptide

Once tRNA is free of its amino acid, it leaves the ribosome to bond onto another amino acid of the correct type in the cytoplasm

The process continues until a terminator codon is reached (tRNA that does not carry an amino acid)

Review

The cellular flow of inherited information is from

a) Protein to RNA to DNA

b) DNA to RNA to Protein

c) DNA to Protein to RNA

d) RNA to DNA to Protein

The cellular flow of inherited information is from

a) Protein to RNA to DNA

b) DNA to RNA to Protein

c) DNA to Protein to RNA

d) RNA to DNA to Protein

When using the Genetic Code to determine the aa sequence in a peptide, one must use the

a) Code sequence from DNA

b) Codon sequence from mRNA

c) Anticodon sequence from tRNA

d) Base sequence from the amino acids

When using the Genetic Code to determine the aa sequence in a peptide, one must use the

a) Code sequence from DNA

b) Codon sequence from mRNA

c) Anticodon sequence from tRNA

d) Base sequence from the amino acids

What is the compliment of a DNA strand with AAGCTT?

a) UUCGAA

b) TTCGAA

c) AACGTT

d) TTCGUU

What is the compliment of a DNA strand with AAGCTT?

a) UUCGAA

b) TTCGAA

c) AACGTT

d) TTCGUU

When the genetic message ATC in DNA causes the synthesis of mRNA with UAG, an amino acid will be delivered to a ribosome by a tRNA molecule bearing

a) TUCb) AUGc) AUCd) ATC

When the genetic message ATC in DNA causes the synthesis of mRNA with UAG, an amino acid will be delivered to a ribosome by a tRNA molecule bearing

a) TUCb) AUGc) AUCd) ATC

Which of the following is NOT true about the Genetic Code?

a) It contains start and stop codons

b) It is different in different types of cells

c) It has 64 different possibilities of base sequences

d) It is composed of a triplet code of three bases per codon

Which of the following is NOT true about the Genetic Code?

a) It contains start and stop codons

b) It is different in different types of cells

c) It has 64 different possibilities of base sequences

d) It is composed of a triplet code of three bases per codon

3.4 Mutations

A gene (point) mutation is an error made during one of the processes that involve base pairing between nucleotides

Chromosome mutations involve segments of chromosomes or entire chromosomes during cell division as in the case of trisomy 21 (down syndrome)

Mutations commonly result from a factor from the environment called a mutagen

Radiation and chemicals are the two most common mutagens

Three types of mutations: deletion, addition, substitution

Deletion

A single nucleotide gets left out

Gene of daughter strand is one nucleotide short

During transcription, the set of triplets from this point on would be incorrect

Addition

Nucleotide is inserted along normal DNA strand

Also incorrect from this point on in the daughter strand

Protein produced is often non functional

Cells often die under this mutation, especially if protein was supposed to be essential enzyme

Substitution

Everything is correct, except one nucleotide replaces another

The mRNA strand produced will contain all the right codons except the one that has been substituted

This MAY affect the incorporation of the correct amino acid into the protein

If a substitution does not change the outcome of the protein produced, then it is degenerative

If the substitution did change the protein (different amino acid), it may never function properly

All proteins are intended for some purpose; mutant proteins may reach their appropriate destination, but fail to function properly

3.5 Recombinant DNA

Recombinant DNA technology allows scientists to insert segments of DNA from one organism into the chromosomes of another

E. coli is a relatively common and harmless human bacterium that is easy to maintain in vitro (in the lab) and it will undergo binary fission about every 20 minutes under good conditions.

Advantages

Producing insulin, growth hormones, interferon (cancer treatment), etc

Certain strains that help environment (oil-metabolizing bacteria)

Production of genetic clones to study differential gene expression

Minimize the effects of genetic errors in humans by removing, repairing and reinserting the gene

Production of hybrid species of some food crops that are disease resistant or more tolerant of extreme environmental conditions

Review

If the normal nucleotide sequence was TACGGCATG, what type of gene mutation is present if the resulting sequence becomes TAGGCATG?

a) Deletion

b) Addition

c) Substitution

d) chromosomal

If the normal nucleotide sequence was TACGGCATG, what type of gene mutation is present if the resulting sequence becomes TAGGCATG?

a) Deletion

b) Addition

c) Substitution

d) chromosomal

Which of the following is NOT a result of addition or deletion of the nucleotide sequence CATUAUCCC?

a) ATUAUCCC

b) CTUAUCCC

c) CATUAUCGC

d) CATTUAUCCC

Which of the following is NOT a result of addition or deletion of the nucleotide sequence CATUAUCCC?

a) ATUAUCCC

b) CTUAUCCC

c) CATUAUCGC

d) CATTUAUCCC

The sequence of nucleotides in DNA that codes for the polypeptide sequence Phe-Leu-Ile-Val is

a) TTG-CTA-CAG-TAG

b) AAA-AAT-ATA-ACA

c) AUG-CTG-CAG-TAT

d) AAA-GAA-TAA-CAA

The sequence of nucleotides in DNA that codes for the polypeptide sequence Phe-Leu-Ile-Val is

a) TTG-CTA-CAG-TAG

b) AAA-AAT-ATA-ACA

c) AUG-CTG-CAG-TAT

d) AAA-GAA-TAA-CAA

The aa phenylalanine, alanine, and lysine exist in a sequence in a particular protein. Which of the following DNA sequences would cause proline to substitute for alanine?

a) AAA-GGG-TTTb) AAA-CGG-TTAc) AAA-CCG-TTTd) AAA-CCC-TTT

The aa phenylalanine, alanine, and lysine exist in a sequence in a particular protein. Which of the following DNA sequences would cause proline to substitute for alanine?

a) AAA-GGG-TTTb) AAA-CGG-TTAc) AAA-CCG-TTTd) AAA-CCC-TTT

Which of these CANNOT be done by recombinant DNA?

a) Changing a person’s genetics

b) Developing hybrid species of food crops

c) Producing clones for scientific investigations

d) Mass producing molecules for medical treatments

Which of these CANNOT be done by recombinant DNA?

a) Changing a person’s genetics

b) Developing hybrid species of food crops

c) Producing clones for scientific investigations

d) Mass producing molecules for medical treatments