Chapter 3 - Guyton Flashcards
Basic building blocks of DNA.
phosphoric acid, deoxyribose (sugar), four nitrogenous bases (2 purines - adenine and guanine; 2 pyrimidines - thymine and ctyosine)
Overview of Transcription
1) RNA polymerase binds to the promoter sequence; 2) RNA polymerase temporarily unwinds the DNA double helix; 3) polymerase reads the DNA strand and adds the complementary RNA molecules to the DNA template; 4) activated RNA molecules react with the growing end of the RNA strand and are added (3’ end); 5) transcription ends when the RNA polymerase reaches a chain terminating sequence, releasing both the polymerase and the RNA strand
Messenger RNA
complementary strand, 100s to 1000s of nucleotides per strand, organized in codons - triplet bases (each codon codes for one AA)
Which amino acid is NOT coded for by multiple codons?
methionine
Start codon
AUG
Stop codons
UAA, UAG, UGA
Transfer RNA
acts as a carrier molecule during protein synthesis, each tRNA combines with one AA, recognizes a specific codon by way of a complementary anticodon on the tRNA molecule
Regulation of Gene Expression by microRNA (miRNA)
primary transcripts of DNA are processed in nucleus by microprocessor complex to form pre-miRNA which are processed in cytoplasm by dicer enzyme, dicer helps to assemble RISC complex and generates miRNAs
How do miRNAs regulate gene expression?
binding to complementary region of mRNA and repressing translation or promoting degradation of mRNA
Messenger RNA
carries the genetic code to
the cytoplasm for controlling the type of protein
formed
Transfer RNA
transports activated amino
acids to the ribosomes to be used in assembling
the protein molecule
Ribosomal RNA
forms ribosomes, the physical
and chemical structures on which protein
molecules are actually assembled
What are polyribosomes?
single messenger RNA molecule can
form protein molecules in several ribosomes at the
same time because the initial end of the RNA strand can pass to a successive ribosome as it leaves the first, clusters are called polyribosomes
Protein formation Phase 1.
Initiation - small ribosomal subunit and initiator tRNA (Met) complex binds to 5’ end of an mRNA chain, this complex moves along mRNA molecule until it encounters a start codon (AUG), initiation factors dissociate and large ribosomal subunit binds
Protein formation Phase 2.
AA-tRNA binds to ribosomal A-site, peptidyl transferase joins the tRNA at the P-site to the AA linked to the tRNA at the A-site with a peptide bond, the new peptidyl-tRNA is translocated from the A-site to the P-site
Protein formation Phase 3.
release factor binds to the stop codon, completed polypeptide is released, ribosome dissociates into its 2 subunits
Genomics
large-scale study of genome, recent studies estimate 30,000 genes, humans are 99.8% identical at the genome level, 99.999% identical in the coding regions
Proteomics
large-scale analysis of proteins, proteome describes the protein composition of a cell, approximately 10,000 proteins per cell or ~15% of total possible gene products
Formation of all the enzymes needed for the synthetic process often is controlled by a sequence of genes located one after the other on
the same chromosomal DNA strand is called what?
operon
Promoter
a group of nucleotides that has specific affinity for RNA polymerase
Repressor operator
a “regulatory” protein can bind here and
prevent attachment of RNA polymerase to the promoter, thereby blocking transcription of the genes of an operon
In some instances, the same
regulatory protein functions as an activator
for one operon and as a repressor for another
operon. When multiple operons are controlled
simultaneously in this manner, all the operons
that function together are called:
regulon
Negative regulation
sequences called repressor operators bind repressor proteins, binding interferes with the ability of the RNA polymerase to bind to the promoter (no transcription)
Positive regulation
activator operators bind activator proteins, binding facilitates the association of the RNA polymerase with the promoter (enhanced transcription)
Eukaryotic cell cycle consists of what?
M phase and Interphase (>95%)
M phase
mitosis and cytokinesis
Interphase
G1, S, (DNA synthesis), G2
DNA Replication (S phase)
switched on by the cytoplasmic S-phase activator, initiated at replication origin and proceeds in both directions, entire genome is replicated once - further replication is blocked, involves DNA polymerase and other proteins that function to unwind and stabilize the DNA and “prime” DNA replication of the “lagging” strand
DNA Replication (S phase) - general characteristics
nucleotides are always added to the 3’ end (DNA and RNA), formation of Okazaki fragments on lagging strand, new DNA is proofread by DNA polymerase, repairs are made and gaps filled by DNA ligase
Histones
nuclear DNA is packaged in specific structural units, the chromosomes which is wound
around small proteins
Centromere
attachment of two chromosomes
Chromatids
chromosome pairs
Mitosis M Phase steps
1) assembly of the mitotic apparatus; 2) prophase; 3) prometaphase; 4) metaphase; 5) anaphase; 6) telophase
What determines the rate of cell growth?
growth factors, contact inhibition, cellular secretions (negative feedback)
Examples of tissues with rapid cell growth.
bone marrow, skin, intestinal epithelia
Examples of tissues with slow/never cell growth.
smooth muscle, neurons, striated muscle
Cell differentiation
different from reproduction in that changes in physical and functional properties of cells occur as they proliferate from selective repression/expression of specific genes, results in development
Cancer
dysregulation of cell growth, caused in all or almost all cases by the mutation or abnormal activation of genes that encode proteins that control cell growth and/or mitosis
Proto-oncogenes
the “normal” genes
Oncogenes
the “abnormal” genes
Antioncogenes
genes whose product suppress the activation of oncogenes
What causes mutations?
ionizing radiation (disrupts DNA strands), chemicals (carcinogens), physical irritants (abrasion of the intestinal linings), hereditary tendencies (some breast cancer), viruses (so-called tumor viruses particularly retroviruses)
Why does cancer kill?
starves healthy cells
Which process is one of the most energy-consuming processes of the cell?
protein formation
These cells reproduce continuously.
blood cells
These cells reproduce every couple of years.
smooth muscle
These cells never reproduce.
neurons and striated muscle
Apoptosis is initiated by a family of proteases called:
caspases
