module 7 bio

DNA

Double-stranded, deoxyribose sugar, bases A, T, G, C; stores genetic info.

RNA

Single-stranded, ribose sugar, bases A, U, G, C; carries info from DNA.

Proteins

Chains of amino acids that perform most cell functions.

DNA location

Nucleus

RNA location

mRNA is made in the nucleus and moves to the cytoplasm.
tRNA and rRNA are in the cytoplasm (ribosomes).

Relationship Between DNA, Genes, Nucleotides, Amino Acids, and Proteins

Genes are DNA segments made of nucleotides.
The nucleotide order determines amino acid order, forming a protein.

Promoter

Where RNA polymerase binds to start transcription.

Coding region

Holds instructions for the protein.

Terminator

Signals transcription to stop.

Transcription process: Initiation

RNA polymerase binds to promoter.

Transcription process: elongation

Builds complementary mRNA strand.

Transcription process: Termination

mRNA and DNA separate.

mRNA Processing Before Leaving Nucleus

• Adds 5’ cap and poly-A tail.

• Removes introns (noncoding).

• Keeps exons (coding).

Alternative Splicing

A process that rearranges or skips exons, allowing one gene to make multiple proteins.

Organelle for Translation

Ribosomes (made of rRNA and proteins) perform translation.

Translation Process: Initiation

Ribosome binds mRNA at start codon (AUG).

Translation process: Elongation

tRNA adds amino acids.

Translation process: termination 

Stop codon ends translation; protein released.

Codon

A group of 3 mRNA bases that codes for one amino acid.

Differential Gene Expression

Cells turn specific genes on or off to make only the proteins they need, enabling cell specialization.

Role of Transcription Factors

• Activators increase transcription.

• Repressors block transcription.

Point Mutation

One nucleotide changes.

Frameshift Mutation

A base added or deleted, shifting the reading frame.

Silent mutaation

No change in amino acid

Missense mutation

Wrong amino acid added.

Nonsense mutation

Early stop codon.

Sources of Mutations

• Errors during DNA replication.

• Exposure to environmental mutagens (radiation, chemicals).

Cell Response to Mutations

• Repair enzymes fix DNA.

• If not fixable: cell stops dividing or undergoes apoptosis (programmed death).