DNADeoxyriboNucleic Acid

DNA!• Makes up

chromosomes

• Contains genes: chunks of DNA that code for certain traits

How can a whole meter of DNA fit into

a tiny cell?

• DNA twists around proteins called histones, to form chromosomes.

• Each segment of between histomes is called a nucleosome.

Watson and Crick

• Discovered structure of DNA in 1953

• long, twisted, double stranded.

• Received Nobel prize for medicine in 1963

• Rosalind Franklin: X-ray images of DNA• She did not receive the Nobel Prize because

she was ineligible (she died in 1958).

NUCLEOTIDES: -building blocks of DNA-made of a a. nitrogenous base (A, T, C, or G), b. sugar (deoxyribose), and c. phosphate.

The Nitrogen Bases

PurinesA = AdenineG = Guanine

PyrimidinesT = ThymineC = Cytosine

DNA BackboneThe DNA backbone is a strand of alternating

sugars and phosphates.The nitrogenous bases (A,T,C, & G) attach at

the sugar site.

DNA Rungs

The rungs of the DNA strand consist of the base pairs and are attached only to the sugar (deoxyribose).

Adenine only pairs with thymine. (A & T)

Cytosine only pairs with guanine. (C & G)

DNA Replication- occurs during interphase. DNA unwinds and each half strand creates a new DNA molecule from loose nucleotides in the nucleus.

• Step 1: Double strand unwinds, and is unzipped by an enzyme (helicase) to create a replication fork

Replication• Step 2: Loose nucleotides join up with

their matching base pairs on both separated strands. Enzymes called DNA polymerases attach the loose nucleotides.

Replication• Result: Two chains formed, each with one

old strand and one new strand.

DNA Replication

1. Enzyme Helicase unzips the DNA molecule

2. Each (half) strand is now a template for a new strand

3. Enzyme DNA Polymerase joins complementary nucleotides to the template strands

4. DNA polymerase also proofreads for mistakes

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Do You Remember Ribosomes??

RibosomesdoProteinSynthesis-creation ofproteins from youramino acidsaccording toyour DNA

Protein Synthesis

• Transcription- to read and write a copy(called RNA) of a section of DNA code for building a protein. Occurs in the nucleus.

• Translation- to translate the RNA code into building proteins from amino acids. Occurs at the ribosomes.

RNARNA is like DNA, a

long sequence of nucleotides.3 main differences

between RNA and DNA

1. The sugar is RIBOSE not deoxyribose

2. RNA is single stranded

3. RNA contains URACIL(U) instead of Thymine (T)

Types of RNA

RNA is involved in protein synthesis.2 main kinds of RNA

1. Messenger RNA (mRNA)- carries genetic messages from nucleus to ribosomes. Length= many letters= one gene

2. Transfer RNA (tRNA)- carries amino acids from cytoplasm to ribosomes. Length= 3 letters

3rd type- Ribosomal RNA (rRNA)

Messenger RNAGenes(sections of DNA) contain instructions

for assembling amino acids. The instructions are carried in messenger RNA(mRNA) with the complementary base:

• C in DNA is carried by G in mRNA. • G in DNA is carried by C in mRNA• T in DNA is carried by A in mRNA• A in DNA is carried by U in mRNA(*RNA has

Uracil instead of Thymine)

The messenger RNA are messengers from DNA to the rest of the cell.

Transcription – DNA to mRNASteps:1.RNA polymerase separates the DNA strands2.RNA polymerase then uses one strand of DNA as a template to make mRNA3.mRNA is released into the cytoplasm.•RNA polymerase always starts at a promoter(start letters) and ends with a terminator(end letters..

Transcription

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mRNA leaves the nucleus to find a ribosome to give its code to and translation begins.

• Translation- translating the mRNA code into building proteins from amino acids. Occurs at the ribosomes.– Amino Acids- the building blocks of

protein molecules. We get them from digesting the protein(meat, etc) we eat

– Codon – a set of 3 nitrogen bases on the mRNA that codes for creation of one amino acid. Ex. GCA codes for the amino acid alanine

Section 12-3

Note that the code for the mRNA codon is complementary to the code for the DNA codon.

There will be one more complementary switch back to the original letters on the tRNA codon (sometimes referred to as the anticodon).

Transfer RNA(tRNA)

During the construction of a protein, a 2nd type of RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA.

These RNA molecules are known as transfer RNA. tRNA codons are sometimes called anticodons.

Translation

(In the cytoplasm)1. mRNA molecule attaches to a

ribosome 2. As each codon moves through the

ribosome, the proper amino acid is brought into the ribosome by tRNA.

3. The amino acid is connected to the growing polypeptide(protein) chain.

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Main Point

DNA Transcription and Translation is

DNA mRNA tRNA Protein

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1) Transcription is DNA converted to mRNA in nucleus

2) Translation is reading the mRNA code at the ribosome, the using tRNA to fetch the proper amino acid.

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Genetic Mutations• Gene Mutations- errors in 1

or more nucleotides in the duplicated DNA sequence. May occur during replication or protein synthesis.– Deletion- 1 base removed

from sequence– Insertion- 1 base added to

sequence– Substitution- 1 base changed

for another base

Genetic Mutations• Chromosome Mutations-

changes in the number or structure of chromosomes. Extra or lost chromosomes and added or deleted sections of chromosomes.– Duplication- extra copy of

section of chromosome– Inversion- reverse the direction

of a section of a chromosome– Translocation- a part of a

chromosome breaks off and attaches to another chromosome.