DNA and Protein Synthesis/Gene Expression

dna structure

double helix, strands in antiparallel direction, held together by hydrogen bonds btw n-bases

nucleotide components

5C sugar, phosphate groups, nitrogenous bases

purines

double ring, adenine/guanine

pyrimidine

single ring, cytosine/uracil/thymine

chargaff’s rule

in dna, %A = %T and %C = %G

semiconservative replication

each original strand serves as a template for the new strand

where does replication occur?

nucleus - S phase

enzymes used in replication?

helicase, dna polymerase, ligase

helicase

unwinds double helix by breaking hydrogen bonds

DNA polymerase

adds nucleotide bases following base pair rules, proofreads

ligase

Joins DNA fragments

nucleosome

chromatin wound tightly around histones

histones

organize chromatin into nucleosomes

where does replication begin?

“origin of replication”

where does transcription occur?

nucleus

transcription

DNA —> mRNA

enzymes used in transcription?

RNA Polymerase

RNA Polymerase

unwinds DNA strands, adds RNA nucleotides

where does transcription begin?

promoter

where does transcription end?

terminator

nuclease

helps proofread, cuts out damaged DNA

where does translation occur?

cytoplasm/ribosomes

where does translation begin?

Start codon/AUG/methionine

where does translation end?

stop codon/UAA, UAG, UGA

Exons

coding regions of a gene

introns

non-coding regions of a DNA

codon

3 nucleotides on mRNA that code for one amino acid

anticodon

3 nucleotides on tRNA complementary to mRNA

mRNA

carries instructions for protein synthesis in the form of codons

tRNA

brings amino acids to ribosome by reading mRNA using anticodons

rRNA

part of ribosome

mutation

random changes in the DNA sequence

Silent Mutation

codon changes but for the same amino acid

missense mutation

codon changes to code for a different amino acid

nonsense mutation

codon changes to a stop codon

frameshift mutation

insertion/deletion, shifts reading frame (most severe)

point mutation

single nucleotide change (silent, missense, nonsense)

Gene expression

DNA → Transcription → mRNA → Translation → Protein