AP Bio Unit 6

Genetic information

Stored as the sequence of bases in DNA and RNA

Chargaff’s Law

In DNA, the amount of adenine equals thymine and cytosine equals guanine

Pyrimidines

Uracil, Cytosine, Thymine – single-ring structures

Purines

Adenine, Guanine – double-ring structures

Prokaryotic Chromosomes

Typically circular with a smaller genome

Eukaryotic Chromosomes

Multiple, linear chromosomes with a larger genome

Plasmids

Small circular DNA molecules; extrachromosomal; found in both prokaryotes (cytosol) and eukaryotes (nucleus)

DNA Replication

Ensures continuity of hereditary information through semiconservative model

Semiconservative Model

Each new DNA molecule has one original strand and one newly synthesized strand

5-prime End

Phosphate terminus of DNA

3-prime End

Hydroxyl terminus of DNA

Antiparallel

DNA strands run in opposite directions

Leading Strand

Synthesized continuously during DNA replication

Lagging Strand

Synthesized discontinuously in fragments during DNA replication

Helicase

Enzyme that unwinds DNA strands

Topoisomerase

Relieves supercoiling at replication fork

Replication Fork

Region where DNA strands are separated

DNA Polymerase

Adds nucleotides in 5’-3’ direction; attaches to 3’ end of template

RNA Primer

Short RNA segment that initiates DNA synthesis

RNA Polymerase

Lays down RNA primers for DNA replication

Ligase

Joins Okazaki fragments on the lagging strand

Transcription

Process of synthesizing mRNA from DNA in the nucleus

Template Strand

Strand used to make mRNA; also called antisense or noncoding strand

Coding/sense Strand

Same sequence as mRNA (except T for U); not used in transcription

mRNA

Carries genetic info from DNA to ribosome

Codon

Three-base sequence on mRNA

tRNA

Carries amino acids to ribosome; matches codons with anticodons

Anticodon

Three-base sequence on tRNA complementary to mRNA codon

rRNA

Makes up ribosomes and catalyzes protein synthesis

Poly-A Tail

Added to 3’ end of mRNA; increases stability and export from nucleus

GTP Cap

Added to 5’ end of mRNA; protects transcript and helps ribosome binding

Introns

Non-coding sequences removed during RNA processing

Exons

Coding sequences retained in mature mRNA

Alternative Splicing

Different combinations of exons spliced to create diverse proteins

Translation

Using mRNA to assemble a polypeptide at the ribosome

Retrovirus

Injects RNA into host; uses reverse transcriptase to make DNA

Reverse Transcriptase

Enzyme that converts viral RNA into DNA

Initiation (Translation)

rRNA binds to mRNA at start codon; tRNA brings first amino acid

Start Codon

AUG; codes for methionine

Elongation (Translation)

tRNA brings amino acids to ribosome; rRNA links them

Termination (Translation)

Stop codon ends translation; polypeptide released

Stop Codon

Codes that do not code for amino acids; end translation

Gene Expression

Process of transcribing and translating DNA into a protein

Regulatory Sequences

Control protein synthesis by promoting or inhibiting transcription

Regulatory Proteins

Bind DNA to enhance or block transcription

Transcription Factors

Regulate transcription and influence cell differentiation

Cell Differentiation

Cells become specialized due to differences in gene expression

Epigenetic Changes

Modifications to DNA/histones affecting gene expression without changing DNA sequence

Histones

Proteins DNA wraps around; can be tightly or loosely packed

Tight DNA Packing

Reduces gene expression by making DNA less accessible

Loose DNA Packing

Enhances gene expression by increasing accessibility

Operon

A cluster of genes under control of one regulatory sequence

Operator

Region where repressor binds to regulate operon

Structural Genes

Code for proteins in operon

Regulatory Gene

Codes for repressor protein

Inducible System

Normally off; can be turned on by an inducer

Repressible System

Normally on; can be turned off by a corepressor

Promoter

Region where RNA polymerase binds to initiate transcription

Coding Region

Genes that are transcribed into mRNA

Repressor

Protein that binds to operator and blocks transcription

Inducer

Molecule that binds and inactivates repressor

Corepressor

Molecule that activates a repressor to shut down transcription

Negative Regulatory Molecule

Inhibits gene expression by blocking transcription

Activator Protein

Enhances gene expression by turning on regulatory genes

miRNA (micro RNA)

Small RNA molecules that degrade or block mRNA translation

Mutation

A change in the genome; may be beneficial, harmful, or neutral

Frameshift Mutation

Caused by insertions/deletions that shift the reading frame

Triploidy

Having three copies of a chromosome

Polyploidy

Having more than two sets of chromosomes

Horizontal Gene Transfer

Movement of genes between organisms other than by inheritance

Transformation

Prokaryote absorbs free DNA from environment

Transduction

Virus transfers DNA from one bacterium to another

Conjugation

DNA is transferred between bacteria through direct contact

Transposition

DNA segments move within and between DNA molecules

Electrophoresis

Technique to separate DNA fragments by size and charge

PCR (Polymerase Chain Reaction)

Amplifies specific DNA segments

Bacterial Transformation

Introduction of foreign DNA into bacteria

DNA Sequencing

Determines order of DNA nucleotides