BIO 130 term 1

• cell is the basic organizational unit of life

• all organisms are comprised of 1 or more cells

• cells arise from pre-existing cells

• no nuclei

• single-celled

• no membrane-bound organelles

• DNA bound by nucleoid(not membrane)

• smaller than eukaryotes

• less DNA than eukaryotes

• Bacteria and Archaea

• nuclei

• single-celled/multicellular

• several membrane bound organelles

• plants, fungi, animals, humans

• plants are larger and more complex

• plants: cell wall, chloroplasts, large vacuole

• aerobic bacterium engulfed by anaerobic eukaryotic cell

• aerobic bacterium loss plasma membrane and split into mitochondria w/ double membrane

• becomes early aerobic eukaryotic cell

• early aerobic eukaryotic cell engulfs photosynthetic bacterium

• photosynthetic bacterium loses membrane and splits into chloroplasts

• becomes photosynthetic eukaryotic cell

• organelles in eukaryotic cells were once prokaryotic microbes that entered eukaryotic cells living together

• shown w/ origins of mitochondria + chloroplasts

1. remnants of mitochondria + chloroplasts’s genomes + genetic systems resemble that of modern day prokaryotes

2. their own protein + DNA synthesis components resemble prokaryotes too

• rapid development w/ short life cycles

• small adult(reproductive) size

• readily available(collections or widespread)

• tractability (ease of manipulation or modification)

• understandable genetics

• E. coli

• Brewer’s yeast

• Arabidopsis thaliana (wall cress)

• Drosophila melanogaster (fruit fly)

• Caenorhabditis elegans (nematode worm)

• Zebrafish

• mice

• prokaryote

• bacteria

• helps show fundamental mechanisms of life (ex: how cells replicate)

• eukaryote

• single celled fungus similar to plant cells (has cell wall, immobile, no chloroplasts)

• simple eukaryote to help study more complex ones

• eukaryote

• weed plant

• helps give insight into development + physiology of crop plants, as well as other plant species

• eukaryote

• fly (insect)

• helps to understand how all animals develop

• eukaryote

• relative of eel worms

• hermaphrodite

• complete genome (959 body cells)

• share genes w/ humans, so helps to see how humans develop

• eukaryote

• transparent first 2 weeks of life

• helps to see how cells behave during development of a living animal

• eukaryote

• used to study mammalian genetics, development, immunology + cell bio.

• study of model organisms helps us to understand humans bc:

• humans can also be studied using:

  1. clinical studies

  2. cell cultures

  3. organoids

• DNA, RNA + proteins synthesized as linear chains of info w/ a definite polarity

• info in RNA sequence is translated into amino acid sequence via genetic code(universal among all species)

• genetic material in a cell(organism’s blueprints)

• DNA = deoxyribonucleic acid

• RNA = ribonucleic acid

1. pentose sugar(foundation for base)

2. nitrogenous base(A, T, C, G, U)

3. phosphate group(backbone, 1-3 P’s)

• nitrogen containing ring compounds

• single ring = pyrimidine (U, T, C)

• double ring = purine (A, G)

RNA:

• ribose sugar

• G, C, A, U

DNA:

• deoxyribose sugar(missing oxygen)

• G, C, A, T

• base + sugar = nucleo__s__ide

• base + sugar + phosphate = nucleo__t__ide

• 1 phosphate = mono, 2 = di, 3 = tri

• DNA synthesized from deoxyribonucleoside triphosphates(dNTPs)

• RNA synthesized from ribonucleoside triphosphates(NTPs)

• nucleotides are linked by phosphodiester bonds

• interactions btwn individual molecules usually mediated by noncovalent attractions

• individually very weak, but can add up to make strong binding btwn molecules

1. electrostatic attractions

2. hydrogen bonds

3. van der waals attractions

4. hydrophobic force

• noncovalent force of attraction between 2 oppositely charged molecules

• similar idea to attractions btwn ions or polar molecules

• in bio. can be seen with regions of positive/negative charges on large molecules

• weaker than covalent bonds

• between hydrogen and really electronegative atom(O, N, F)

• allows for special properties of water

• weakest force of attraction

• nonspecific interaction, can happen in all types of molecules

• similar types of forces interacting w/ e/o(hydrophobic w/ hydrophobic)

• helps to promote molecular interactions

• important for building cell membrane

• holds DNA double helix shape together

• A - T has 2 hydrogen bonds

• G - C has 3 hydrogen bonds

1. hydrogen bonds

2. hydrophobic interactions

3. van der Waals attractions

• energetically favourable conformation

• proteins can recognize + make contact w/ specific DNA sequences in major + minor grooves

• 2 strands are complementary

• can be unzipped

• antiparallel (one strand is 5’→3’, other is 3’→5’)

• end of 5’ made of phosphate group(PO4)

• end of 3’ made of hydroxyl group(OH)

• can be separated by proteins in cell + heat

important for:

• DNA replication

• RNA synthesis

• subunits of proteins

• Types of amino acids:

1. acidic (important for enzymes)

2. basic (important for enzymes)

3. uncharged polar (h-bonds in water)

4. nonpolar (insides of proteins, may be present in lipid bilayers)

• alpha carbon

• carboxyl group

• amino group

• R group(what decides amino acid)

• has disulfide bonds

• non polar amino acid

• forms btwn carboxyl group + amino group of diff. amino acids

• R groups r not involved

• causes polypeptide chain to have amino end(N terminus) + carbonyl end(C terminus)

• water as product(condensation reaction)

• has N-terminal + C-terminal

• R groups r not involved

• hydrogen bonds btwn every 4 amino acids(residue)

• R groups are not involved (but alternately project up + down)

• usually contains 4-5 beta strands, but can have 10+

• H-bonding btwn carbonyl oxygen (C=O) + amine hydrogen (N-H) of 2 diff. amino acids in neighbouring strands

• anti-parallel

• parallel

• atoms in bonding: carbonyl oxygen + amine hydrogen in peptide backbone

• Alpha helices: h-bonding every 4 AA’s apart within polypeptide chain

• Beta sheet: btwn AA’s in diff. segments/strands of polypeptide chain

• multiple alpha helices tied together

• amphipathic (has both hydrophilic + hydrophobic parts)

• found in alpha-keratin of skin, hair + myosin motor proteins

• overall 3D structure of a protein

• proteins fold into conformation that is most energetically favourable

• protein shape dictated by amino acid sequence aided by chaperone proteins

• held together by:

  1. hydrophobic interactions

  2. non-covalent bonds

  3. covalent disulfide bonds

• helps the process of protein folding more efficient + reliable

1. backbone model: shows overall organization of polypeptide chain

2. ribbon model: shows folding patterns

3. wire model: shows R groups’ positions

4. space filling model: shows protein surface

• regions of polypeptide chain that are able to independently fold into tertiary structure

• domains specialized for diff functions

• important for evolution of proteins

• common evolutionary origin

• have similar aa sequences + tertiary structures

• members evolved to have diff functions

• most proteins belong to families w/ similar structural domains

• hemoglobin protein formed from separate subunits: 2 α, 2 β

• each subunit = separate polypeptide chain

• sickle cell anemia caused by mutation in

  β subunit

Can be:

• many identical subunits(proteins)

• mixtures of diff proteins + DNA/RNA (more diverse in function w/ diff protein subunits)

• dynamic assemblies of proteins to form molecular machines

1. purify protein(s) of interest using electrophoresis/chromatography

2. determine amino acid sequence (using mass spectrometry)

3. discover precise 3D structure

• Proteomics(large scale study of proteins)

• can come in all sizes(size not always correlated w/ # of genes/organism complexity)

• includes all DNA including non-coding regions

Repeated sequences(~50%):

• simple repeats

• segment duplications

• mobile genetic elements:

  1. LINEs

  2. SINEs

  3. retrotransposon

  4. DNA-only transposon

Unique sequences(~50%):

• nonrepetitive DNA(neither introns/exons)

• introns (transcribed, not translated)

• exons (codes for proteins) (~1.5% of genome)

• DNA condensed through folding + twisting, complexed w/ proteins (genome very big w/o packing)

• forms the prokaryotic nucleoid

Challenge:

• human genome very very big**(no personality, smh)**

Solution:

• packing DNA into chromosomes

• uses idea of complementary strands + able to unzip strands

• looks for particular sequence in chromosome(DNA probe hybridizes with chromosome DNA)

• 23 pairs in humans(last pair for sex of human)

• made of chromatin

• replicated in interphase + M phase

• held together at centromere

• ends are called telomeres

• single, long, linear DNA molecule + associated proteins

• tightly packaged but remains assessible for transcription, replication, + repair

• is DYNAMIC(on how tightly packed it is)

• made of 8 different nucleosomes

2 phases:

• interphase

• M phase(mitosis)

Interphase:

• gene expression + chromosome duplication

M phase:

• mitosis

• chromosome separated

• made of DNA wrapped around histones

• ~6 packed histones make 1 nucleosome

• small proteins rich in lysine + arginine

• positive charge able to neutralize negative charge of DNA

• 4 core histone proteins:

  1. H2A

  2. H2B

  3. H3

  4. H4

• pair of each in octamer core

• 1 linker histone(H1)

• non-histone clamp proteins involved in forming chromatin loops

performed by:

• chromatin remodeling complexes

• histone modifying enzymes

Can cause:

• heterochromatin

• euchromatin

• Highly condensed chromatin

• areas where gene expression is suppressed

examples:

• meiotic + mitotic chromosomes

• centromeres + telomeres

• one X chromosome in females(Barr body)

• relatively non-condensed chromatin

• areas where genes tend to be expressed

• DNA synthesis is semiconservative(only one seen in nature so far)

• Always occurs from 3’ end to 5’ end(DNA polymerase stitching)

• Growth occurs from 5’ end to 3’ end

3 possible models:

1. unidirectional growth of single strands from 2 starting points

2. unidirectional growth of 2 strands from 1 starting point

3. bidirectional growth from 1 starting point

• Where DNA replication begins

Characteristics:

• easy to open, rich in A-T bonds(less h-bonds)

• recognized by and binding of initiator proteins occurs

# of origins of replications:

• 1 in bacteria

• multiple in Eukaryotes

• bidirectional growth from 1 starting point

• this style of replication only applies to circular genomes

• is asymmetrical

Causes:

• 2 strands

  1. lagging strand: replicated discontinuously(causes Okazaki fragments)

  2. leading strand: replicated continuously

1. binds to origin

2. helps helicase bind

3. requires ATP

Performed by:

• 2 types of helicases

• predominant one moves along lagging strand template(5’→3’)

Requires:

• a lot of ATP

• binds single stranded DNA(ssDNA) to separate strands

• prevents strands from H-bonding, reannealing, hair pins, and loops until replication occurs

• synthesize RNA primers needed for DNA polymerase to bind

• proceeds(reads) in 3’→5’ along template strand

• reads 3’→5’ along parent strand

• creates DNA in 5’→3’ direction

• removes 2 phosphates from nucleoside triphosphate to add onto growing strand

• holds polymerase onto DNA

• seals nick(gap) caused by removal of RNA primers

• helicase + primase

Problem:

• as helicase unwinds DNA, supercoiling + torsional strain increases

• problem in circular chromosomes + large linear eukaryotic chromosomes

Solution:

• solved by DNA topoisomerase (breaks phosphodiester bond and reseals it)

Problem:

• major problem for lagging strand

• loss of sequence information on 5’ end on daughter strand

Solution:

• repetitive sequence added to the 3’ end of parent strand determined by RNA template in telomerase

• RNA template

• resembles reverse transcriptase

• generates G-rich ends

• adds nucleotides to 3’ ends to parental strand template

• telomerase are abundant in stem and germ-line cells, but not in somatic cells

• loss of telomeres during DNA replication, limits # of time cell can divide

• Most cancer cells produce high level of telomerase

• if mistake during replication not repaired, mutation occurs and stays in new generations

RNA polymerases:

• has error rate ~1 in 1000

DNA polymerases:

• has error rate ~1 in 1000000000

• human genome(3 bill. bp) only changes ~3 nucleotides every time a cell divides

Function:

• removes misincorporated nucleotide

• performed by DNA polymerase(polymerizing section(P) + editing section(E)

• DNA pol. detects helix distortion and moves back 1 space to remove nucleotide

• error repair process(when proofreading fails)

• initiated by direction of distortion in geometry of double helix generated by mismatched base pairs

• even after synthesis, DNA can get damaged + need repair

• defects in repair mechs., linked w/ variety of human diseases

Types of damage:

1. oxidation

2. radiation

3. heat

4. chemicals

• and other cell stressors

Depurination:

• loss of purines(A,G) in nucleotide

• causes deletion mutation

Deamination:

• loss of amine(NH2) group on cytosine(C)

• converts C to U

• improper base pairing mutation

1. base excision repair: fixes smaller problems(1 base removed)

2. nucleotide excision repair: removes multiple nucleotides(ex: dimers)

Two situations:

1. nonhomologous end joining: results in some loss of nucleotides at repair site

2. homologous end joining: results in no loss of nucleotides at repair site

• Segments of DNA that are transcribed into RNA

• Types of genes when transcribed:

  1. RNA that encodes for a protein(mRNA)

  2. RNA that functions as RNA and may not be translated into protein(tRNA + rRNA)

• RNA nucleotides added in 5’→3’ (anti-parallel)

• uses ssDNA as template(other ssDNA is coding strand)

• RNA nucleotides linked by phosphodiester bonds

• DNA-RNA helix held by base pairing

• no need for primers

• just needs the temple

• less accurate than DNA pol.(more mistakes)