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CH 25 DNA
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CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Dec 22, 2015

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Page 1: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

CH 25DNA

Page 2: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Monomer of Nucleic Acids

A molecular complex of three types of subunit molecules

1. Phosphate

2. Pentose sugar

3. Nitrogen-containing base

NUCLEOTIDES

Page 3: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA (deoxyribonucleic acid)

Stores genetic material

Codes for the order in which AA are joined to form a protein

RNA (ribonucleic acid)

Conveys DNA’s instructions regarding the amino acid sequence in a protein

3 types:

1. Messenger RNA

2. Ribosomal RNA

3. Transfer RNA

NUCLEIC ACIDS

Page 4: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA RNA

Sugar Deoxyribose Ribose

Bases Adenine, Guanine, Thymine, Cytosine

Adenine, Guanine, Uracil, Cytosine

Strands Double Stranded (with base pairing) Single Stranded

Helix Yes No

NUCLEIC ACIDS

Page 5: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA is double-stranded with

complementary base pairing

A-TC-G

DNA STRUCTURE

Page 6: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Purines:

Adenine and Guanine

Two rings

Found in DNA and RNA

Pyrimidines:

Cytosine, Thymine, Uracil

One ring

Cytosine found in DNA and RNA

Thymine found in DNA only

Uracil found in RNA only

NUCLEOTIDES

Page 7: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

In the mid-1900s, scientists knew that chromosomes, made up of DNA (deoxyribonucleic acid) and proteins, contained genetic information.However, they did not know whether the DNA or

the proteins was the actual genetic material.

HISTORY

Page 8: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Various researchers showed that DNA was the genetic material when they performed an experiment with a T2

virus.

By using different radioactively labeled components, they demonstrated that only the virus DNA entered a bacterium

to take over the cell and produce new viruses.

HISTORY

Page 9: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

VIRAL DNA IS LABELED

Page 10: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

VIRAL CAPSID IS LABELED

Page 11: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

The structure of DNA was determined by James Watson and Francis Crick in the early 1950s.

They deduced the following:• DNA has a twisted, ladder-like structure

(double helix)

• The sugar-phosphate molecules make up the sides of the ladder and the bases make up the

rungs

• Since A bonds with T and G with C, the rungs have a constant width

(purine paired with a pyrimidine)

DNA STRUCTURE

Page 12: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

BASE PAIRING

Page 13: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

TWO DNA STRANDS ARE ANTI-PARALLEL – THEY RUN IN OPPOSITE

DIRECTIONS.

Page 14: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA replication occurs during chromosome duplication;

an exact copy of the DNA is produced with the aid of

DNA polymerase (an enzyme)

Hydrogen bonds between bases break and enzymes “unzip” the molecule.

Each old strand of nucleotides serves as a template for each new strand.

REPLICATION

Page 15: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

New nucleotides move into complementary positions are joined by DNA polymerase.

The process is semiconservative because each new double helix is composed of an old strand of

nucleotides from the parent molecule and one newly-formed strand.

REPLICATION

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Page 17: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

LADDER CONFIGURATION & DNA REPLICATION

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1. ‘DNA: Structure, function and replication’ - WS

2. ‘DNA’ notes booklet3. ‘Protein Synthesis’ – WS

4. CH 2 Review Q’s

TO WORK ON:

Page 19: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

25.2GENE EXPRESSION

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A gene is a segment of DNA that specifies the amino acid sequence of a protein.

Gene expression occurs when gene activity leads to a protein product in the cell.

A gene does not directly control protein synthesis; instead, it passes its genetic information on to RNA, which is more

directly involved in protein synthesis.

GENE EXPRESSION

Page 21: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Bases: Adenine-Uracil, Cytosine-Guanine

Types:

1. Messenger RNA (mRNA): takes message from DNA to ribosome

2. Ribosomal RNA (rRNA): along with proteins, makes up the ribosomes – where proteins are

synthesized

3. Transfer RNA (tRNA): transfers amino acids to the ribosomes

RNA

Page 22: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

RNA STRUCTURE

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1. Transcription: makes an RNA molecule complementary to a portion of DNA

2. Translation: occurs when the sequence of bases of mRNA directs the sequence of amino

acids in a polypeptide

PROTEIN SYNTHESIS

Page 24: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA specifies the synthesis of proteins because it contains a triplet code: every three bases stand for

one amino acid.

Each three-letter unit of an mRNA molecule is called a codon.

Most amino acids have more than one codon; there are 20 amino acids with a possible 64 different

triplets.

The code is nearly universal among living organisms.

THE GENETIC CODE

Page 25: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

MRNA CODONS

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GENE EXPRESSION

Page 27: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves

as a template for mRNA formation.

RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to

the triplet code in DNA.

TRANSCRIPTION

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Page 29: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA contains exons and introns.

Before mRNA leaves the nucleus, it is processed and the introns are excised so that only the exons

are expressed.

The splicing of mRNA is done by ribozymes, organic catalysts composed of RNA, not protein.

Primary mRNA is processed into mature mRNA.

PROCESSING OF MRNA

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Page 31: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Translation is the second step by which gene expression leads to protein synthesis.

During translation, the sequence of codons in mRNA specifies the order of amino acids in a

protein.

Translation requires several enzymes and two other types of RNA: transfer RNA and

ribosomal RNA.

TRANSLATION

Page 32: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

During translation, transfer RNA (tRNA) molecules attach to their own particular amino

acid and travel to a ribosome.

Through complementary base pairing between anticodons of tRNA and codons of mRNA, the

sequence of tRNAs and their amino acids form the sequence of the polypeptide.

TRNA

Page 33: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

TNA: AMINO ACID CARRIER

Page 34: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Ribosomal RNA, also called structural RNA, is made in the nucleolus.

Proteins made in the cytoplasm move into the nucleus and join with ribosomal RNA to form the

subunits of ribosomes.

A large subunit and small subunit of a ribosome leave the nucleus and join in the

cytoplasm to form a ribosome just prior to protein synthesis.

RRNA

Page 35: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

A ribosome has a binding site for mRNA as well as binding sites for two tRNA molecules at a time.

As the ribosome moves down the mRNA molecule, new tRNAs arrive, and a polypeptide forms and

grows longer.

Translation terminates once the polypeptide is fully formed; the ribosome separates into two subunits

and falls off the mRNA.

Several ribosomes may attach and translate the same mRNA, therefore the name polyribosome.

RIBOSOMES

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POLYRIBOSOME

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During translation, the codons of an mRNA base-pair with tRNA anticodons.

Protein translation requires these steps:1) Chain initiation

2) Chain elongation3) Chain termination.

Enzymes are required for each step, and the first two steps require energy.

TRANSLATION: 3 STEPS

Page 38: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

During chain initiation, a small ribosomal subunit, the mRNA, an initiator tRNA, and a large

ribosomal unit bind together.First, a small ribosomal subunit attaches to the

mRNA near the start codon.The anticodon of tRNA, called the initiator RNA,

pairs with this codon.Then the large ribosomal subunit joins.

CHAIN INITIATION

Page 39: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.
Page 40: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

The initiator tRNA passes its amino acid to a tRNA-amino acid complex that has come to the

second binding site.

The ribosome moves forward and the tRNA at the second binding site is now at the first site, a

sequence called translocation.

The previous tRNA leaves the ribosome and picks up another amino acid before returning.

CHAIN ELONGATION

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Page 42: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Chain termination occurs when a stop-codon sequence is reached.

The polypeptide is enzymatically cleaved from the

last tRNA by a release factor, and the ribosome falls away from the mRNA molecule.

A newly synthesized polypeptide may function alone or become part of a protein.

CHAIN TERMINATION

Page 43: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.
Page 44: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

DNA in the nucleus contains a triplet code; each group of three bases stands for one amino acid.

During transcription, an mRNA copy of the DNA template is made.

The mRNA is processed before leaving the nucleus.

The mRNA joins with a ribosome, where tRNA carries the amino acids into position during

translation.

REVIEW

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Page 46: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

A gene mutation is a change in the sequence of bases within a gene.

MUTATIONS

Page 47: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

Frameshift mutations involve the addition or removal of a base during the formation of mRNA; these change the genetic message by shifting the

“reading frame.”

FRAMESHIFT MUTATION

Page 48: CH 25. Monomer of Nucleic Acids A molecular complex of three types of subunit molecules 1.Phosphate 2.Pentose sugar 3.Nitrogen-containing base NUCLEOTIDES.

The change of just one nucleotide causing a codon change can cause the wrong amino acid to be inserted in a

polypeptide; this is a point mutation.

In a silent mutation, the change in the codon results in the same amino acid.

If a codon is changed to a stop codon, the resulting protein may be too short to function; this is a nonsense

mutation.

If a point mutation involves the substitution of a different amino acid, the result may be a protein that cannot reach

its final shape; this is a missense mutation.

An example is Hbs which causes sickle-cell disease.

POINT MUTATIONS

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SICKLE CELL DISEASE

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Mutations can be spontaneous or caused by environmental influences called mutagens.

Mutagens include radiation (X-rays, UV radiation), and organic chemicals (in cigarette smoke and

pesticides).

DNA polymerase proofreads the new strand against the old strand and detects mismatched

pairs, reducing mistakes to one in a billion nucleotide pairs replicated.

CAUSE & REPAIR OF MUTATIONS

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Transposons are specific DNA sequences that move from place to place within and between

chromosomes.

These so-called jumping genes can cause a mutation to occur by altering gene expression.

It is likely all organisms, including humans, have transposons.

TRANSPOSONS: JUMPING GENES