Download Modification of Genes and Proteins - sharonap-cellrepro-p2

Do not press any buttons during the presentation, it will progress on its own.
Transcript Processing
 Protein Folding
 RNAi
 Gene Repair

Transcription factor recognizes TATA Box
and binds to DNA
 RNA polymerase bonds to DNA
 RNA polymerase separates strands and
strings together complementary
nucleotides (using U instead of T)
 Primary transcript has been created
when terminator region is reached


Transcription:
› Creates molecule to carry protein
instructions from DNA
› Creates exact replica complementary to
DNA

Alteration of ends of transcript:
› 5’ end capped with modified guanine
 Keeps RNA from degrading in the cytoplasm
› Cleavage factors and stabilizing factors bind
to 3’ end
› Poly A polymerase binds and cleaves 3’ end
and adds poly A tail made of adenine

RNA splicing:
› Nucleotides removed
› Introns = non-coding regions
› Exons = coding regions to be expressed
› Small nuclear ribonucleoproteins (snRNPs) =
proteins that detect adenine at branching
site
› Spliceosomes remove the intron and bind
the two exons

The sequence of amino acids defines a
protein’s primary structure.

Blueprint for each amino acid is
characterized by base triplets
› Found in the coding region of genes

Ribosomes recognize triplets and
create proteins
Covalent bonds between
amino acids help stabilize
the protein
 Shape and stability also
maintained by chemical
forces


Chaperone proteins:
› Prevent nearby proteins from inappropriately
›
›
›
›
associating and interfering with proper
folding
Surround protein in protective chamber
during folding
Ex) bacteria: GroEL and GroES
Use ATP
Also assist in refolding proteins
Chaperone proteins protecting folding proteins

Models of protein folding:
› Diffusion Collision Model:
 Nucleus is formed
 Secondary structures collide and pack
together
› Nuclear Condensation Model:
 Secondary and tertiary structures are made
simultaneously

RNAi = RNA Interference
› Also known as:
› Cosuppression
› Post Transcriptional Gene Silencing
› Quelling

RNAi is used to:
› Silence specific genes
› Fix gene expression problems in mammals

Types of small silencing RNA:
› Small interfering RNA (siRNA)
 Endogeneous: derived from cell
 Exogeneous: delivered by humans
› Micro RNAs (miRNA)
› PIWI-interacting RNAs (piRNA)

RNAi breaks up mRNA before it is synthesized.

Allows singling out of genes to determine
function.

Could halt progression of:
› Cancer
› HIV
› Arthritis
› All other diseases

DNA can be damaged by:
› Radiation (gamma, x-ray, and ultraviolet)
› Oxygen radicals from cellular respiration
› Environmental chemicals (hydrocarbons)
› Chemicals used in chemotherapy

Four major types of DNA damage:
› Deamination: amino acid group lost
› Mismatched base
› Backbone break
› Covalent cross-linkage between bases
Deamination in DNA

Repairing damaged bases:
› Direct chemical reversal
› Excision repair mechanisms:
 Base excision repair (BER)
 Nucleotide excision repair (NER)
 Mismatch repair (MMR)

Chemical Reversal
› Ex) glycosylase enzymes remove
mismatched T and restore correct C

Excision repair mechanisms:
› Base excision repair:
 DNA glycosylases identify damaged bases
 DNA glycosylases remove damaged bases
 Deoxyribose phosphate backbone
component removed, creating gap
 Gap filled with correct nucleotide
 Break in strand ligated

Excision repair mechanisms:
› Nucleotide excision repair:
 Protein factors identify damage
 DNA is unwound
 Faulty area is cut out and the bases are
removed
 DNA is synthesized to match that of the
opposite, correct strand
 DNA ligase adds synthesized DNA

Excision repair mechanisms:
› Mismatch repair
 Corrects mismatches of normal bases (A&T,
C&G) by:
 Identifying mismatched bases
 Cutting mismatched bases
Any Questions?