Bio Mini Quiz

replication

DNA copying

transcription

DNA-\>RNA

translation

RNA-\>protein

Steps of protein synthesis Advanced

RNA made from DNA as a template

RNA is spliced into mRNA (introns (nonsense RNA) taken out, exons kept)

mRNA is moved outside the nucleus to the ribosome

Codons on mRNA is matched up with anticodons on tRNA

tRNA codons carry an amino acid based on its triplets

The amino acid is added to the growing chain of amino acids creating a protein

When finished the amino acid chain leaves the ribosome and is moved to its target area.

Mutation

A change in the DNA code that changes the protein being made

Can be beneficial, detrimental or neutral

Spontaneous mutations = natural reaction in the organism (no cause)

Induced mutation = due to exposure to UV-light, chemicals or other environmental agent

Are normally permanent

Can be inherited, but not always

**Point mutation**

Change in one single base in the DNA sequence

Also known as single substitution

mutation

**Substitution mutation**

Can be a single point mutation (previous slide)

Can be several bases

**Inversion**

When a part/segment of a mutation is reversed

**Insertion**

When a new base or segment is added in

Causes a frameshift, which

makes the protein different

**Deletion**

When a base or a segment is removed

Causes a frameshift

Silent mutation

No change in the amino acids/proteins being produced

Missense mutation

The amino acid sequence changes

Nonsense mutation

Creates a STOP in the amino acid sequence, which gives a change in function

Frameshift mutations

changes where the reading of the code starts and ends and can change the amino acid chain/protein dramatically

**Steps of Protein synthesis simplified**

Transcription: the DNA sequence/gene is copied, substituting T for U

Translation: the mRNA sequence is matched in the ribosome with tRNA carrying an amino acid. Bases are read as triplets.

mRNA

Messenger RNA, is the copy of the gene, produced/found in the nucleus, flat shape

tRNA

Transfer RNA, is the link between mRNA and amino acids, carried one amino acid, found in cytoplasm, hairpin shape

rRNA

Ribosomal RNA, found in the ribosome, part of the ribosome’s structure, globular

**RNA modification**

Before going on to the ribosome the RNA needs to be modified.

Introns are being spliced out, exons are expressed so they are kept.

Spliceosome is responsible for splicing.

Alternative splicing: gives a single gene an option to make several different proteins.

mRNA Protection

The mRNA has to be protected from digestive enzymes in the cytoplasm. Does this in two ways:

Capping: addition of modified guanine, protects from digestive enzymes, helps attach to the ribosome

**RNA Messaging Key**

Introns removed- REFINES MESSAGE!

Alternative Splicing -MAXIMIZE MESSAGE -to create different protein recipes from same mRNA.

Capping and Tailing – PROTECTS THE MESSAGE!

**Translation Stages**

Initiation: tRNA starts the coding based on the start codon - AUG

Elongation: amino acids are joined together one-by-one with covalent bonds

Termination: a stop signal is reached on the mRNA and the new polypeptide chain detaches.

Stop codons: UAA, UAG, UGA 

Codes that starts with a U it is most likely a stop codon

Codons

a mechanism where the message is read in triplets – what we call “codons”

Codon – the triplet of bases on the mRNA that correspond to a particular amino acid

Anti-codon – the complimentary triplet of bases on tRNA that brings a specific amino acid to the ribosome

**Gene Regulation**

Only 2% of the human genome actually codes for something, as far as we know

A lot of DNA seems to have come from viruses

This explains the need for splicing

**Promoters and enhancers**

Promoter sequences: non-coding DNA, longer

“Shows” where transcription for RNA starts

Very often known as the TATA box

Located 25-35 bases away from the start of the actual gene

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Enhancer sequence: non-coding DNA, shorter

Enhances the rate of transcription = makes transcription faster