MHS Biology – Test 4: Molecular Genetics Study Guide

Griffith’s contribution to DNA discovery

Discovered bacterial transformation; showed that genetic material could be transferred between cells

Hershey and Chase’s contribution to DNA discovery

Used bacteriophages to prove that DNA (not protein) is the genetic material

Chargaff’s contribution to DNA discovery

Discovered that A = T and C = G in DNA

Watson and Crick’s contribution to DNA discovery

Built the first accurate model of DNA as a double helix

Rosalind Franklin’s contribution to DNA discovery

Used X-ray diffraction to reveal the helical structure of DNA

What is a nucleotide

The basic unit of DNA made of sugar, phosphate, and nitrogen base

What are purines

Adenine and Guanine (double-ring bases)

What are pyrimidines

Cytosine and Thymine (single-ring bases)

What is complementary base pairing

A-T and C-G pairing rules in DNA

What is the double helix

The twisted ladder shape of DNA

What is DNA helicase

Enzyme that unwinds and unzips DNA

What is DNA polymerase

Enzyme that builds new DNA strands

What is the first step of DNA replication

DNA helicase unzips the DNA

What happens after DNA unzips

DNA polymerase adds complementary nucleotides

How does DNA replication end

Two identical DNA molecules are formed

What is ribonucleic acid (RNA)

Single-stranded nucleic acid that helps make proteins

What is transcription

Process of making mRNA from DNA

What is mRNA

Messenger RNA that carries code to ribosome

What is RNA polymerase

Enzyme that builds RNA during transcription

What is the promoter region

Region of DNA where transcription begins

What is translation

Process of building a protein from mRNA

What is a codon

A three-base sequence on mRNA that codes for an amino acid

What is the start codon

AUG – signals start of protein synthesis

What is a stop codon

UAA, UAG, or UGA – signals end of protein synthesis

What is tRNA

Transfer RNA that brings amino acids to ribosome

What is an anticodon

Three-base sequence on tRNA that matches mRNA codon

What is a mutation

A change in DNA sequence

Steps of protein synthesis

DNA → transcription → mRNA → translation → protein

Where does transcription occur

Nucleus

Where does translation occur

Ribosome in cytoplasm

What happens in transcription

mRNA is made from DNA template

What happens in translation

tRNA brings amino acids to build protein

Difference between DNA and RNA

DNA is double-stranded, RNA is single-stranded

Sugar in DNA

Deoxyribose

Sugar in RNA

Ribose

Base unique to DNA

Thymine

Base unique to RNA

uracil

Location of DNA

Nucleus

Location of RNA

Nucleus and cytoplasm

How do you transcribe DNA to mRNA

Use complementary base pairing (A→U, T→A, C→G, G→C)

How do you translate mRNA to protein

Use codon chart to match codons to amino acids

What amino acid does AUG code for

Methionine (start)

What is a silent mutation

Mutation that does not change amino acid

What is a missense mutation

Mutation that changes one amino acid

What is a nonsense mutation

Mutation that creates a stop codon

What is a frameshift mutation

Adding or deleting nucleotides shifts reading frame

What can cause mutations

Radiation, chemicals, errors in replication

Effect of missense mutation

May change protein function

Effect of nonsense mutation

Protein is shortened, often nonfunctional

Effect of frameshift mutation

Completely changes protein sequence