review: dna, transcription & translation. structure dna code for proteins double stranded helix...

Review:DNA, Transcription

& Translation

StructureDNA

• Code for proteins• Double Stranded Helix• Can NOT leave nucleus• Made of Sugar

(deoxyribose), Phosphate & nitrogen base– Thymine– Adenine– Guanine– Cytosine

RNA• Copy of the code for

proteins• Transports code to

Ribosome• Single Stranded• Can leave nucleus• Made of Sugar (ribose),

Phosphate & nitrogen base– Uracil– Adenine– Guanine– Cytosine

Replication• Occurs in nucleus.

• DNA makes a copy of itself.

T

A

C

G

G

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C

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G

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G

Transcription• Occurs in nucleus.

• DNA makes a mRNA copy of the code.

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U

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C

G

Translation

• Occurs at Ribosome.

• mRNA binds with tRNA to build an amino acid chain or protein.

Every 3 letters represents one amino acid or

codon.

Example: GUU = Valine

Summary

Mutations

• Any change in DNA sequence is called a mutation.

• Mutations can be caused by errors in replication, transcription, cell division, or by external agents.

Mutations

• Mutations can be harmful.– Sickle cell anemia

– Cystic fibrosis

•Mutations can be beneficial.–Phenotypic (physical) changes

–Flower color–Fur color

Mutations

• Mutations can occur in both types of cells:– Body cells (muscle, skin, brain, bone etc)

– Gametes (Sex Cells – sperm or egg)

Skin Cells Sperm Cell & Egg Cell

• Damage to a gene may impair the function of the cell.

• When that cell divides, the new cells also will have the same mutation.

• This can result in the cells growing and dividing rapidly, producing cancer.

Mutations in body cells• If a body cell’s DNA is changed, this mutation would

not be passed on to offspring.

• Mutations that occur in the gametes or sex cells can be passed on to the offspring.

Mutations in Gametes

• A point mutation is a change in a single base pair in DNA.

• A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein.

Types of Mutations

THE DOG BIT THE CAT.

THE DOG BIT THE CAR.

• An example of a point mutation, is sickle-cell disease.

• Sickle-cell diseases cause the red blood cells to be deformed. The result is that they get stuck in the blood vessels, depriving tissues of oxygen, causing strokes, and blood clots.

Types of Mutations

What would happen if a single nitrogenous base (letter) is deleted?

THE DOG BIT THE CAT.

THD OGB ITT HEC AT.

• A mutation in which a single base is added or deleted from DNA is called a frameshift mutation.

• Sometimes during mitosis or meiosis chromosomes break and then rejoin incorrectly, or just a piece breaks off for good.

• Structural changes in chromosomes are called chromosomal mutations.

Chromosomal Alterations

Deletion- part is missing

Insertion- part breaks off and attaches in the wrong place

Inversion- part breaks off and attaches upside down

Translocation- breaks off and attaches to different chromosome

• Occurs during meiosis, when chromosomes fail to separate properly.

Non-Disjunction

• Normal humans have:– 46 chromosomes

• 22 pair of Autosomes• 1 pair of Sex

chromosomes• Non-Disjunction:

– Too many chromosomes?

– Too few?– 47 or 45

chromosomes

Normal karyotype

Is this a male or female?

Down Syndrome• Also called Trisomy 21

– 3 chromosomes instead of 2

• Some mutations seem to just happen, perhaps as a mistake in base pairing during DNA replication.

• These mutations are said to be spontaneous.

• However, many mutations are caused by factors in the environment, such as radiation, chemicals, and even high temperatures.

– Ex: Chernobyl explosion

Causes of Mutations

• Any agent that can cause a change in DNA is called a mutagen.