AP Bio Unit 6

DNA

Double-stranded helix molecule composed of nucleotide monomers and each strand is anti-parallel to the other (5’ to 3’ on one and 3’ to 5’ end on another)

Nitrogenous bases

Adenine binds to Thymine through hydrogen bonds as does Guanine and Cytosine

DNA vs RNA

DNA is seen in all cell-based organisms while RNA is seen in viruses

RNA is involved in protein synthesis and regulation of gene expression while DNA is involved in none

Prokaryotes

• Looped circular chromosomes

• DNA is packaged in naked DNA

• contains plasmids

Eukaryotes

• Multiple linear chromosomes

• DNA is wrapped around proteins called histones

• Do not contain plasmids

DNA Replication

The process where a cell makes an exact copy of its DNA before dividing

(Occurs in the nucleus during S-phase)

Helicase Step in DNA Replication

An enzyme, helicase, unwinds the double helix into two single-strands by breaking hydrogen bonds, creating a replication fork that allows for replication to happen

Primase Step in DNA Replication

The enzyme primase adds short RNA primers to the strand so that the DNA polymerase knows where to start copying

DNA Polymerase Step in DNA Replication

An enzyme DNA polymerase binds new nucleotides to each strand but in different manners:

To the leading strand: It builds it continuously without stopping in the same direction of replication fork

To the lagging strand: Builds it discontinously using Okazaki fragments, which are short segments of DNA set up by primase

Types of RNA

mRNA, rRNA, and tRNA

mRNA

brings instructions from DNA to ribosomes

rRNA (Ribosomal RNA)

Makes up catalytic part of ribosomes and binds amino acids together during protein synthesis

tRNA (Transfer RNA)

Brings specific amino acids to the ribosomes for protein synthesis

Transcription

• Occurs in the nucleus

• RNA polymerase binds to DNA and makes a copy of it in the form of mRNA

• This mRNA leaves the nucleus and heads toward the cytoplasm

Translation

• Occurs in the cytoplasm, specifically on ribosomes

• once mRNA has arrived to ribosome, ribosome reads mRNA in codons

• Each codon tells the ribosome which amino acid that tRNA should bring in

• Ribosome links amino acids together to build a protein

Key parts of Ribosomes

• Large subunit: catalytic site where peptide bonds are formed

• Small subunit: decoding site where codons are read

• A-site: where aminotacyl-tRNA binds

• P-site: where peptidyl-tRNA binds

Initiation in Transcription

RNA polymerase binds to the promoter on DNA

Elongation in Transcription

RNA polymerase reads the DNA and adds RNA bases (A, U, C, G) to make a growing mRNA strand

Termination in Transcription

RNA polymerase reaches a stop signal in the DNA: releases mRNA and DNA zips back up

Initiation in Translation

Ribosome binds to start of mRNA at a specific codon (usually AUG)

Elongation in Translation

Ribosome reads each mRNA codon, and tRNA brings matching amino acid

Termination in Translation

Ribosome reaches stop codon, no more amino acids are added

Operons

Group of genes that are located next to each other on DNA, controlled together by a promoter, and transcribed into one big mRNA

(If genes are the lamps and promoters are the on/off switch, operons are the power strip where promoters can turn on and off and express genes)

Promoters

DNA sequences where RNA polymerase binds to initiate transcription

Introns

Interfering sequences of DNA within genes that are transcribed into pre-mRNA but not translated

Exons

DNA sequences that become RNA, then mRNA, then translated into protein

mRNA Processing

• 5’ GTP Cap: protects mRNA from breaking down by enzymes

• 3’ Poly-A Tail: Increases mRNA stability

• Introns are excised

RNA Splicing

Pre-mRNA is made during transcription containing both introns and exons, but spliceosomes recognize and excise introns and joins exons together, forming a clean and mature mRNA

Alternative Splicing

Exons can be spliced and allow for multiple protein versions from same pre-mRNA transcript

Silent Mutation

A change in the DNA sequence that doesn’t affect resulting amino acid in protein

(If GAA becomes GAG, it still codes for Glu)

Missense Mutation

Point mutation that changes one amino acid in the protein sequence

Nonsense Mutation

Changes a codon from an amino acid into a STOP codon

Frameshift Mutation

Insertion/deletion of a nucleotide that shift the whole protein sequence

Conjugation

Two bacteria cells link together through pilis and one cell sends a plasmid to the other, getting all the genes of the donor bacterial cell

Transformation

A bacterial cell dies and a bacterial cell can swipe the materials from the dead cell and has it for its own