Biology ~ DNA Replication

Chromosomes coiled structures are made up of DNA and proteins.

When the DNA is not coiled it exists as a grainy substance called chromatin.

The DNA of a chromosome is encoded with genetic instructions for making proteins. 

Humans have 2 SETS of 23 chromosomes, a TOTAL of 46 chromosomes.

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Nitrogen bases:

PURINES

• Adenine and Guanine

PYRIMIDINES 

• Cytosine and Thymine

A=T

C=G

Nitrogen bases are held together by weak hydrogen bonds. 

Hydrogen bonds are easily broken.

Nucleotides are held together by strong covalent bonds.

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RNA + DNA differences:

1. RNA is made up of ribose sugar, DNA is made up of deoxyribose sugars. DNA is a double helix while RNA is only single. RNA includes the nitrogen base Uracil instead of Thymine while DNA does not. 

2. They can both be found in a cell's nucleus and help in the process of making proteins.

DNA REPLICATION

1. Enzyme Helicase unzips the DNA into two strands. 

2. Enzyme DNA Polymerase adds complementary nucleotides to the template strands.

• Primase

– Required for DNA synthesis

– Like a “key” for a car ignition

– Makes short RNA primers

• Short pieces of RNA to help get the DNA polymerase started

• DNA polymerase

– adds nucleotides to RNA primer (1st function)

– After all nucleotides are added to complement strand RNA

primer is removed and replaced with DNA by DNA polymerase

(2nd function)

– Proofreads the strand before the backbone is finished (3rd

function)

• DNA ligase

– “seals” the gaps in DNA

– Connects DNA pieces by making phosphodiester bonds

3. Two identical DNA molecules are formed, each with an “old”

strand and a “new” strand. We call this Semi-Conservative

Replication (because part of the molecule is

conserved/saved.)

Messenger RNA (copies genetic instructions from DNA to cytoplasm), Transfer RNA (brings amino acids to ribosomes), and Ribosomal RNA (helps form ribosomes)

The process in which cells make proteins is called protein synthesis. There are two stages with this: transcription and translation.

Transcription - It is the transfer of genetic instructions in DNA to messenger RNA (mRNA). 

3 steps:

 Initiation  - It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases.

Elongation - During this process, an adenine (A) in the DNA binds to an uracil (U) in the RNA.

Termination - occurs when RNA polymerase crosses a stop (termination) sequence in the gene. The mRNA strand is complete, and it detaches from DNA.

Splicing removes introns from mRNA 

Editing changes some of the nucleotides in mRNA

Polyadenylation adds a “tail” to the mRNA. 

Translation - (occurs in the ribosomes) reads the genetic code in mRNA and makes a protein.

Characteristics of Genetic Code

-Universal, all known living organisms use the same genetic code

-Unambiguous, each codon codes for just one amino acid

-Redundant, most amino acids are encoded by more than one codon

There are 20 common amino acids in proteins.