Bio Chapter 18

DNA

• governs hereditary traits

• Within nucleus

• Double strand

• Deoxyribose sugar

RNA

• protein synthesis and gene expression

• Within nucleus and cytoplasm

• Single strand

• Ribose sugar

Nucleotide

• building block of DNA

• Made of sugar, phosphate and nitrogen base

• Sugar differentiates RNA and DNA

Sugar-phosphate link

Part of the nucleotide that forms the backbone of DNA

Complementary Bases

• bases that are always linked to each other

• Appear in equal proportions

Antiparalell

• nucleotides are arranged antiparalell

• Dependant on carbons

• 3’ end and 5’ end

DNA Replication

• occurs during interphase (synthesis)

• semi conservative replication

• New strand is created in opposite direction

Initiation

• Helicase unwinds DNA by breaking hydrogen bonds

• Replication fork forms

• Occurs in many places simultaneously

Helicase

• enzyme

• Acts as an unwinder for DNA

• Turns single strand into double strand

Elongation

• DNA Polymerase is inserted, adds nucleotides

• Creates a complementary strand (complementary bases)

• Primase inserts RNA Primer

Primase

• inserts RNA primer, nucleotide starting point

Primer

• a short strand of RNA that is starting point for new nucleotides

Leading Strand

• replicated continuously

• 5’ to 3’ direction

Lagging strand

• replicated in short segments

• Nucleotides added in 5’ to 3’ direction

  • Synthesized in short bursts (Okazaki fragments)

Okazaki Fragments

• the short bursts of lagging strand synthesis

Ligase

• enzyme that glues together the Okazaki fragments

• Glues together recombinant DNA

Termination

• strand is complete

• Machine is dismantled

Genetic Hierarchy (least to most specific)

Genome, chromosome, gene (locus), allele

Genome

• sum of genetic information of an organism

Chromosome

• tightly wound bundle of chromatid

• Long DNA molecules

Gene

• short stretches of DNA that encode a specific trait

• Located at a specific locus

Allele

• the exact trait that is expressed

• 2 alleles

Proteins

• made of amino acids

• Sequence determines chemical properties

• Determine structure function and properties of the cell

Codon

• set of three nucleotides

Genetic Code Characteristics

• degenerate ( redundant)

• Continuous

• Universal

Degenerate (redundant)

• contains multiple codons per amino

Continuous

No spaces between codons

Universal

Protein synthesis through use of codons is common for organisms

Central Dogma

DNA

Transcription in nucleus via mRNA

Translation in cytoplasm with tRNA

Protein

Transcription

• 1st step of gene expression

• Reading DNA

Sense Strand

• the strand not transcribed

• Same sequence as mRNA

Anti-sense strand

• the strand of DNA that is transcribed the template

RNA polymerases

• Synthesis of RNA from 5’ to 3’ direction

Promotor

• sequence of nucleotides on DNA

• Tells RNA polymerase where to bind to sense strand and make mRNA

Translation

• mRNA takes the transcribed information into the RER

tRNA

• what mRNA is transcribed onto

• Contains anticodons

Anticodons

Stretch of three nucleotides on the tRNA that are complementary to the codons

Germ mutations

• passed down through reproductive cells

Somatic cell mutation

key cause of cancer

Point mutation

Small change to one or more nucleotides

Silent mutation

One nucleotide is substituted, but the same amino acid is produced

Mis-sense mutation

• a DIFFERENT amino acid is coded

Non-sense

No amino acid is coded from genetic information

Frame shift mutations

• Insertion and deletion

• Far more dangerous

Insertion

New nucleotide is added, shifts everything right

Deletion

Nucleotide is added, shifts everything left

Spontaneous mutation

• completely random, molecular mistakes

Induced mutation

Caused by mutagens I.e. alcohol, nicotine

Mitochondrial DNA

• small DNA circles that are found within the mitochondria

• Entirely maternal

Endosymbiosis Theory

• the idea that mitochondria were once free floating prokaryotes that were then absorbed

• Created eukaryotes

Plasmid

• DNA within bacteria

• separate from chromosome, replicates independently

Restriction enzyme

catalyses cleavage of DNA at certain nucleotide sequences

Restriction endonuclease

• the sequence that dictates where the cut is

• Forms “sticky ends” to attach to other fragments

Genetic Engineering

• manipulate genetic material to alter and splice

Gel electrophoresis

• dna is put in a gel and the strands separate based on length

Mutagenesis

• exposing something to mutagens intentionally

• i.e. UV radiation

Chorionic villi sampling

• early in pregnancy

• Samples placenta cells

Amniocentesis

Sample cells from amniotic fluid