IB Biology Topic 2.6-2.7 Topic 7.1-7.3 - PowerPoint Presentation

Slide1

IB Biology

Topic 2.6-2.7 Topic 7.1-7.3

Structure of

DNA and RNA

DNA Replication

Transcription & Translation

Nucleotides

3 major nucleic acids:

DNA, RNA, ATP

DNA & RNAMade of nucleotides (monomer)Nucleotides:One phosphateOne 5 carbon monosaccharideOne nitrogenous base

Bases:

Adenine

Guanine

CytosineThymineUracil in place of thymine in RNAPurines and Pyrimidines:

Monomers

 Polymers

Backbone:

Alternating pentose-phosphate Bases extend outward Order of bases determine genetic code for organismCovalent bonding between components

Single or Double Strand

RNA- always SS

A-U, G-C

DNA always DSBases are paired: complementary base-pairingA-T, G-CHydrogen bonds between bases

Anti-Parallel Arrangement

Deoxyribose + phosphate= phosphodiester bond (linkage)

Forms between hydroxyl group of 3’ carbon of deoxyribose and phosphate group to 5’ carbon of deoxyribose

New always added to 3’ carbon endResult: Double strand has 2 directions

DNA Packaging

Paired with histone proteins for organization

Nucleosome-

2 molecules of each of 4 different histones (8 histones total)DNA- (-) charge and histones (+) chargeBetween nucleosomes, often a 5th histone attached to linking string of DNAAdditional histone

 supercoiling

DNA Packaging, cont.

Supercoiling of DNA makes it inaccessible to transcription enzymes

Form of regulation

Only certain areas of DNA involved in protein synthesis

Types of DNA Sequences

Highly Repetitive sequences:

5-300 base pairs

100,000 replicates of a certain type per genomeClustered in discreet areas- satellite DNADispersed throughout-Coding function not known

Types of DNA Sequences, cont.

Protein Coding Genes

Provide base sequences

 proteins via ribosomesBase sequences carried from the nucleus to the ribosomes via mRNAGenes not fixed sequence of bases, but coding info (exons) mixed with non-coding fragments (introns)

Types of DNA Sequences, cont.

Structural DNA:

Highly coiled- has no coding function

Around centromere and near ends of chromosomesPseudogenes: lost coding function due to mutation involved with a base change

Types of DNA Sequences, Cont.

Short tandem repeats and DNA Profiling:

Most of our DNA is identical to every other human

Specific regions that show variation: polymorphismsPolymorphisms are used for DNA profilingLook at 13 specific loci: short tandem repeats (STRs) of 2-5 base pairs

Semi- C

onservative

R

eplicationWatson and CrickStructure of DNASingle strand of DNA used as templateMeselson and StahlConfirmed findingsBacterial DNA replication process developed as result

Bacterial DNA:

Circular

No histone proteins

Single point of origin for replication of DNA

Eukaryotic DNA:

Linear

Has histones

Has thousands of points of origin

Semi-Conservative Replication, cont.

Replication steps:

1. Begins at origin, appears as a “bubble”

2. Helicase unzips H bonds between bases.3. End of bubble replication fork4. Bubbles enlarge in both directions and eventually fuse to produce 2 identical daughter strands

https://

www.youtube.com/watch?v=dKubyIRiN84

DNA Replication

Elongation of DNA strand

1. Primer produced by

primase at replication forkPrimer is 5-10 nucleotides of RNAPrimase allows joining RNA nucleotides that match DNA sequence

2.

DNA polymerase III

allows the addition of nucleotides in a 5’ to 3’ direction

3.

DNA polymerase I

removes primer from 5’ end and replaces it with DNA nucleotides

4.

Topoisomerase (DNA gyrase)

stabilizes

DNA above helicase

DNA Replication, cont.

Anti-Parallel

strands

One 5’ 3’, one 3’ 5’DNA only assembled in 5’  3’ direction due to DNA pol III.3’ 5’ template strand made quickly and continuously-

leading strand

5’ and 3’ template strand made discontinuously and in pieces-

lagging strand

Pieces are called

Okazaki fragments

Fragments are joined by

DNA ligase

DNA Replication, cont.

1.

Leading strand

assembled continuously2. Lagging strand assembled in Okazaki fragments3. Primer, primase, and DNA pol III

required to begin formation of each

O

kazaki fragment

4.

Primer and primase

needed only once for leading strand

5.

DNA ligase

attaches sugar-phosphate backbone together

Replication Proteins

Replication in prokaryotes and eukaryotes is almost identical

Speed and Accuracy of Replication

4000 nucleotides per second

Bacteria-

Speed essential, divide every 20 minutesRemarkably accurate-Few errors occurCells have repair enzymes that detect errorsRepair enzymes also used when cells are damaged by chemicals or high energy waves

Replication, DNA Sequencing, Human

G

enome

ProjectHGP required actual representation of nucleotide sequence in humans.Sequencing DNA-1970s Sanger developed sequencing procedureFragments of DNA copied through PCR (polymerase chain reaction)

Read and outline section on

page 332-333

bring

questions to class.