DNA Replication & Protein Synthesis

DNA

The genetic material (genome) found principally in chromosomes.

Deoxyribonucleic acid

The nucleic acid of all life.

Chromatins

Make up long fine threads that chromosomes exist in in between cell divisions.

Chromosomes

• In between cell divisions they exist in long fine threads of chromatin,

• When a cell is about to divide, chromosomes coil and condense.

• Where DNA is found principally.

DNA structure

A sequential series of joined nucleotides which consist of:

• Sugar (deoxyribose)

• Phosphate

• Base (A, T, C, G)

DNA replication

Occurs during chromosome duplication.

1. Replication

DNA serves as its own template

2. Replication

Hydrogen bonds between strands break and the molecule unzips (helicase).

3. Replication

New nucleotides fit beside parental strand.

4. Replication

DNA polymerase joins new nucleotides.

5. Replication

Two complete molecules are now present, each with one old strand and one new strand.

Helicase

An enzyme that acts like a zipper, unwinding the double helix structure of DNA into two separate strands during DNA replication.

DNA polymerase

An enzyme that joins new nucleotides during DNA replication.

Ribonucleic acid (RNA)

Another type of nucleic acid where the sugar molecule has an extra oxygen molecule compared to DNA.

Hydrogen bonds

Can form within the RNA strand, resulting in folds.

RNA structure

Made up of nucleotides containing:

• Ribose (sugar)

• Uracil (base) in place if thymine

Single stranded.

RNA function

A helper to DNA, allowing protein synthesis.

DNA-RNA similarities

• Both are nucleic acids

• Both are composed of nucleotides

• Both have a sugar-phosphate backbone

• Both have four different types of bases

DNA differences

• Found in the nucleus

• The genetic material

• Sugar = deoxyribose

• Bases = A, T, C, G

• Double stranded

• Is transcribed, to give mRNA

RNA differences

• Found in nucleus and cytoplasm

• Helper to DNA

• Sugar = ribose

• Bases = A, U, C, G

• Single stranded

• Is translated, to give proteins

Ribosomal RNA (rRNA)

• A primary component of the ribosome, and is responsible for its catalytic activity.

• Joins with proteins made in the cytoplasm to form the subunits of ribosomes.

Messenger RNA (mRNA)

• A transcript copy of a gene which encodes a specific polypeptide

• Carries genetic information from DNA to the ribosomes in the cytoplasm where protein synthesis occurs.

Transfer RNA (tRNA)

• Transfers amino acids to the ribosomes where amino acids are joined.

Proteins structure

• Composed of amino acids (20 types).

• Differ because the number and order of their amino acids differ.

How proteins are made

1. Transcription

2. Translation

3. Folding

1. Transcription

Process in protein production where the genetic instructions are copied from the DNA to the mRNA molecule.

2. Translation

The production of a protein using the information that is coded in the mRNA molecule.

3. Folding

The process in protein production where the protein strand is folded into the correct structure for function.

Gene

A sequence of DNA along a chromosome that codes for a protein.

• Contains a triplet code

• Every three bases represents = one amino acid

Transcription

• DNA serves as template for mRNA. Strand of mRNA forms that is complementary to a portion of DNA.

• Uracil present in mRNA instead of thymine

• The triplet of mRNA = codon

Transcription step 1

Helicase unzips the double-stranded DNA, exposing nucleotides in some DNA, which is called the template strand.

Template strand

The strand of a DNA molecule that is used to form the sequence of bases in mRNA and is copied during transcription.

Transcription step 2

RNA polymerase attaches to the strand of DNA at promoter sequence.

Transcription step 3

The RNA polymerase will ‘copy’ the DNA template by added C, G, U, A using complementary base pairing. The mRNA strand will be identical to the coding strand except the mRNA will have U instead of T.

Transcription step 4

Nucleotides are added to the mRNA until it reaches a terminator sequence.

Transcription step 5

mRNA moves out of the nucleus through a nuclear pore.

Translation

• The synthesis of a polypeptide under the direction of an mRNA molecule.

• Transfer RNA molecules bring amino acids to the ribosomes (translators).

• Anticodon (on tRNA) is a triplet complimentary to an mRNA codon.

Translation step 1

Ribosome binds with start codon on mRNA (AUG).

Translation step 2

tRNA carrying an amino acid contains anticodon that binds to complimentary mRNA codon.

Translation step 3

Ribosome moves along adding amino acids to the chain.

Translation step 4

Ribosome reaches stop codon (UAG, UAA, or UGA) and releases amino acid sequence.

Translation step 5

Amino acid sequence folds to create 3D shape called protein.

Chain of nucleotides

What tRNA is made up of, they pair up with each other to give the molecule a characteristic shape.

Anticodon

The tight loop halfway down the tRNA’s chain of nucleotides that contains three bases that can interact with the mRNA. The tRNA carries the amino acid that matches this.