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Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 PowerPoint PPT Presentation

Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: 931-6325 Email: [email protected] CHEM1020/General Chemistry _________________________________________ Chapter 15. (L17)-Biochemistry

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Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221

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Department of Chemistry

CHEM1020 General Chemistry

***********************************************

Instructor: Dr. Hong Zhang

Foster Hall, Room 221

Tel: 931-6325

Email: [email protected]


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CHEM1020/General Chemistry_________________________________________Chapter 15. (L17)-Biochemistry

  • Today’s Outline

    …Structures of DNA

    Double helix

    Higher levels of structures

    …Structure of RNA

    …DNA self-replication

    …RNA: Protein synthesis and the genetic code

    …Genetic engineering


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Chapter 15. (L17)-Biochemistry

  • Structures of DNA

    …DNA can have several levels of structures much like proteins.

    …The 1st level: the sequence of organic bases in the nucleotides of DNA polymers.

    …All the genetic information is stored by means of the base sequence.

    The four bases can make up almost uncountable combinations in a long huge DNA chain with MW of billions for mammals.


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Chapter 15. (L17)-Biochemistry

  • Structures of DNA

    …DNA can have several levels of structures much like proteins.

    …The 2nd level: Double-Helix

    Observations: the molar amount of A is equal to the molar amount of T, and similarly for G and C.

    Conclusion: A has to pair with T, and G has to pair with C.

    Now, the question is how the bases are paired?

    The double-helix model proposed by James Watson and Francis Crick in 1953.


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Chapter 15. (L17)-Biochemistry

  • Structures of DNA

    …DNA can have several levels of structures much like proteins.

    …The 2nd level: the Double-Helix model for DNA

    -two right-handed DNA helix wound about one another.

    -the phosphate and sugar backbone of the polymer chains form the outside of the structure like a spiral staircase.

    -the amine bases are paired on the inside with G-C and T-A pairing, and the paired bases are like steps of the staircase.

    -elegant hydrogen bonding between the two paired bases

    ..always a purine base (G or A) paired with a pyrimidine base (C or T)

    ..both pairs have the same long dimension, and the length is 1.085 nm

    -the hydrogen bonding fitted with the bases like lock and key


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Chapter 15. (L17)-Biochemistry

  • Structures of DNA

    …DNA can have several levels of structures much like proteins.

    …The 2nd level: the Double-Helix model for DNA

    Significance of the Double-Helix DNA model

    -it answers so much crucial questions in biochemistry

    -it explains how cells are able to divide and functioning, how genetic data are passed on to new generations, and even how proteins are built to required specifications. It all is determined by the base paring and the base sequence.


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Chapter 15. (L17)-Biochemistry

  • Structures of DNA

    …DNA can have several levels of structures much like proteins.

    …The 2nd level: the Double-Helix model for DNA

    Other forms of DNA double-helix

    Three forms of DNA double-helix-B form, most common, long, right-handed

    -A form, less common, short, right-handed

    -Z form, less common, long, left-handed


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Chapter 15. (L17)-Biochemistry

  • Structures of RNA

    …RNA polymers generally have the structure of single strands

    -some internal base pairing may occur in sections where the polymer folds back on itself

    -portions of the polymer may exist in double-helix.


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Chapter 15. (L17)-Biochemistry

  • DNA self-replication

    …A gene is a section of the DNA molecule

    …Process of DNA self-replication

    -the original DNA double-helix opens up or “unzip” itself

    -then, a new nucleotide is brought into the position of one single DNA polymer chain to pair with the specific base by the enzyme of DNA polymerase)

    -then, one more nucleotide is brought in and the phosphate ester linkage is made to connect the two new nucleotides

    -the above process goes on and on to form a new double-helix using one of the original two helix polymer chain of the particular DNA

    -each original helix chain serves as a template (blueprint)


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Chapter 15. (L17)-Biochemistry

  • RNA protein synthesis

    DNA stays only in the cell nucleus. But, the genetic information has to be carried to the other places of the cell.

    …Transcription: DNA transfers its information to a special RNA molecule called messenger RNA or mRNA;

    -the base sequence of the DNA specifies the base sequence of the mRNA by pairing of G vs. C and A vs. U.


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Chapter 15. (L17)-Biochemistry

  • RNA protein synthesis processes

    -mRNA gets the genetic information by transcription

    -mRNA attaches itself to a ribosome which is composed of RNA and proteins and enzymes for protein synthesis

    -tRNA (transfer RNA) carries amino acids from the cell fluid to the ribosomes

    -a specific tRNA then matches its triplet base code (anticodon) with the base triplet of the mRNA (codon) through the base-pairing (G-C or A-U)

    -then the amino acid required by the condon on the mRNA will be put into the protein chain being synthesized via the peptide bond formation at the ribosome

    -there are 61 different tRNA molecules, each for one of the 20 amino acids

    -only the tRNA with the right code match by the base pairing can provide the amino acid required by the mRNA

    -once the tRNA provides the matched amino acid and after it is installed in the protein chain, the tRNA will leave the ribosome and will get a fresh amino acid

    -mRAN has three codons that cannot be matched with any tRNA for any amino acids, called termination base triples or codons; once the ribosome goes to the position of the mRNA with anyone of the three termination codons, then the ribosome stops the protein synthesis


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Chapter 15. (L17)-Biochemistry

  • RNA protein synthesis processes: Possible errors and consequences

    -each time a human cell divides, 4 billion bases are copied to make a new strand of DNA, and there may by up to 2000 errors occurring, a chance of 0.5 in 1000,000

    -most of the errors are corrected, and others are unimportant

    -but, some errors can be terrible or fatal, the reason for genetic diseases


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Chapter 15. (L17)-Biochemistry

  • Genetic code

    …The genetic code is a three base combo called base triplet on the mRNA

    -doublet has combinations of 2 letters out of four bases for RNA, which gives 4x4 = 16 different doublet codes, insufficient codes for 20 amino acids

    -triplet has combinations of 3 letters out of four bases for RNA, which gives 4x4x4 = 64 different triplet codes, enough codes for 20 amino acids

    -quadruplet has combinations of 4 letters out of four bases for RNA, which gives 4x4x4x4 = 256 different triplet codes, too many codes for 20 amino acids

    …Genetic code table


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Chapter 15. (L17)-Biochemistry

  • Genetic engineering

    …The Human Genome Project

    …Genetic testing

    -PCR technique: Polymerase Chain Reaction, using bacterial enzymes called DNA polymerases to produce a large quantities of the same DNA extracted from a sample so that enough amount of the same DNA samples can be obtained to perform the DNA sequencing

    -The DNA is sequenced by using enzymes to cleave it into segments of about 500 nucleotides each

    -DNA sequence comparison

    -DNA figureprinting technology

    …Recombinant DNA technology

    …Gene therapy


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Chapter 15. (L17)-Biochemistry

  • Genetic engineering

    …Pros and cons

    Controversy vs. promises

    beyond science

    duty of citizens


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Chapter 15. (L17)-Biochemistry

Quiz Time

The DNA sequence is the sequence of

(a) the phosphates of the DNA nucleotides;

(b) the sugars of the DNA nucleotides;

(c) the bases of the DNA nucleotides;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The first level of the DNA structure is

(a) pleated DNA polymer chains;

(b) folding of the DNA polymer chain;

(c) the sequence of the bases of the DNA nucleotides;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The secondary level of the DNA structure is

(a) pleated DNA polymer chains;

(b) folding of the DNA polymer chains like spiral helixes;

(c) the sequence of the bases of the DNA nucleotides;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The helix structure of a DNA is

(a) in the form of single-helix;

(b) in the form of double-helix;

(c) in the form of triple-helix;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The double-helix structure of a DNA is formed by folding of

(a) left-handed double-helix;

(b) right-handed double-helix;

(c) one right-handed and one left-handed double-helix;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The double-helix structure of a DNA is formed mainly by which type of bonding?

(a) magnetic attraction between two bases;

(b) ionic bonding between two bases;

(c) hydrogen bonding between two bases;

(d) dispersion force between two molecules.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The base pairing between the two helix stands of the double-helix structure of the DNA is

(a) random;

(b) specific;

(c) varying depending on the time;

(d) varying depending on the temperature.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The double-helix structure of a DNA is formed through the bonding or pairing between bases of

(a) G and T and A and T;

(b) G and T or A and C;

(c) G and C or T and A;

(d) G and C and T and C.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The DNA replicates itself by

(a) cutting itself into various small pieces and then growing of each small piece to a full new double-helix;

(b) cutting itself into two half double-helix and then the elongation of each half;

(c) splitting the double-helix and then each single helix will form a new DNA by cooperating with a new helix strand formed by DNA polymerase;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

In protein synthesis, the sequence of the amino acids in a protein polymer is determined ultimately by

(a) random chance;

(b) the location of the synthesis;

(c) the temperature of the synthesis;

(d) the sequence of the bases in the DNA.


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Chapter 15. (L17)-Biochemistry

Quiz Time

In protein synthesis, the sequence of the bases of the DNA is first transferred to

(a) an enzyme;

(b) tRNA, called transfer RNA;

(c) mRNA, called messenger RNA;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The function of mRNA is

(a) to bring the bases of the DNA to the place for protein synthesis;

(b) to get the base sequence information from the DNA in the nucleus and then carries the base sequence information with it to the outside of the nucleus where the amino acids are available for protein synthesis; and then it will direct the protein synthesis;

(c) to help DNA self-replication;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The process for an mRNA to get the base sequence information from the DNA and carries the information to the place where proteins are synthesized is called

(a) transfer;

(b) translation;

(c) transcription;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

The tRNA means and its function is, respectively

(a) translation RNA and to transfer the genetic information from one protein to another;

(b) transfer RNA and to bring a specific amino acid to ribosome in which a protein is synthesized;

(c) transport RNA and to transport proteins in the cell;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

Each tRNA carries a specific amino acid identified and dictated or controlled by

(a) the overall base sequence of the tRNA;

(b) the –R group of the amino acid;

(c) the three bases on one arm of the folded tRNA, called anticodon;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

In synthesis of a protein, its amino acid sequence is determined by means of

(a) matching a triplet base sequence on the DNA with the triplet base sequence on one arm of the tRNA called anticodon through the base pairing;

(b) matching a triplet base sequence on the mRNA, called codon, with the triplet base sequence on one arm of the tRNA called anticodon through the base pairing;

(c) matching the –R group of the specific amino acid carried by the tRNA with the base sequence on the mRNA;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

A genetic code means

(a) a triplet base sequence on the tRNA;

(b) a triplet base sequence on the mRNA;

(c) a triplet base sequence on the DNA;

(d) a quadruplet base sequence on the mRNA.


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Chapter 15. (L17)-Biochemistry

Quiz Time

Three genetic codes that do not designate any amino acids are

(a) the wasted codes;

(b) the termination or “stop” codes;

(c) the codes for any amino acids;

(d) none of above.


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Chapter 15. (L17)-Biochemistry

Quiz Time

Generally, outside the nucleus, protein synthesis involves which of the following necessary biochemical components?

(a) mRNA and tRNA only;

(b) mRNA, tRNA, ribosome, and amino acids;

(c) mRNA, tRNA, and ribosome;

(d) mRNA, ribosome, and amino acids.


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Chapter 15. (L17)-Biochemistry

Quiz Time

Certain errors in DNA self-replication may cause

(a) a change in hand-writing style;

(b) infectious diseases;

(c) genetic diseases;

(d) a change in color preference.


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