DNA, RNA, and Protein Synthesis: Key Concepts and Processes

Sugar in DNA

Deoxyribose

Four bases in DNA

A, T, C, G

Type of bonds between bases across strands

Hydrogen bonds

Number of DNA strands used as template

Both (each original strand)

Replication template

Parental DNA strand

Replication product

Two identical DNA double helices

Why is there a lagging strand?

DNA polymerase can only build 5′→3′, so one strand must be made in Okazaki fragments

A binds with

T (two hydrogen bonds)

C binds with

G (three hydrogen bonds)

Helicase

Unwinds DNA double helix

Primase

Makes short RNA primers

DNA polymerase III

Main DNA synthesis enzyme

DNA polymerase I

Replaces RNA primers with DNA

DNA ligase

Seals gaps between Okazaki fragments

Sugar in nucleotide

Ribose

Four bases in RNA

A, U, C, G

Template in transcription

DNA strand (template strand)

Product of transcription

Single-stranded RNA (mRNA)

Is a primer used in transcription?

No

Are prokaryotic mRNAs processed?

No (no cap, tail, or splicing)

What are introns and exons?

Introns: noncoding; Exons: coding regions kept in mature mRNA (eukaryotes)

Sigma factor

Helps RNA polymerase find the promoter

Promoter

DNA sequence where RNA polymerase binds to start transcription

Shine-Dalgarno sequence

Ribosome-binding site in prokaryotic mRNA upstream of start codon

Codon definition

3-base mRNA sequence coding for one amino acid

How many bases are in a codon?

Three

Difference between free and bound ribosomes

Free: cytosol proteins; Bound: make secreted/membrane proteins on ER

tRNA function

Brings amino acids and matches codon with anticodon

First amino acid added to a protein

Methionine (start codon AUG)

What happens at the A site

New tRNA with amino acid enters and matches codon

What happens at the P site

Holds growing peptide chain and forms peptide bond

What happens at the E site

Empty tRNA exits ribosome

Wobble definition

Flexibility at 3rd codon base; allows some mismatches without changing amino acid

Polyribosome definition

Several ribosomes translating one mRNA simultaneously

Monomer of a protein

Amino acid

Translation template

mRNA strand

Translation product

Polypeptide/protein

What types of RNA are involved in translation?

mRNA, tRNA, rRNA