Cell Bio Flashcards
(34 cards)
Total protein produced by genes in lifetime
About 100,000 proteins
What are functiona of microRNA, small interefering RNA, small nuclear RNA
MiRNA are formed in cytoplasm from pre-miRNA regulate gene expression and block translation siRNA cause degradation of mRNA and also regulate gene expression snRNA helps in splicing of mRNA
RNA polymerase
Synethesize mRNA from DNA
Does not require primer
1) binds to promoter region
2) breaks H-bonds and uncoils DNA
3) adds new nucleotide by breaking p bonds of old nucleotide and from this energy does make covalent bonds to new nucleotide
4) at termination points it gets removed and thus mRNA . H bonds of mRNA break Both dna strands attach back because they have high affinity
RNA polymerase enzymes
RNA polymerase I: most rRNA (5.8S, 18S, 28S)
- RNA polymerase II: mRNA
- RNA polymerase III: rRNA (5S),
RNA door name meer
2 RNA polymerase inhibitors
RNA Polymerase Inhibitors
- Rifampin
- Inhibits bacterial RNA polymerase
- Used to treat tuberculosis
- Actinomycin D
- Used as chemotherapy
- Inhibits RNA polymerase
Promoters
Non-transcribed DNA portion where RNA and transcription factors attach e-g Promoters * Very common eukaryotic promoter TATA Box * TATAAA Binds transcription factors (TFIID) *CCAAT sequence CAAT Box GC Box GGGCGG
Silencer
Enhancer
Silencers
• DNA sequence that decreases rate of transcription
*Binds transcription factors called repressors
*^Repressors prevent RNA polymerase binding
Enhancers
DNA sequences that increase rate of transcription
Binds transcription factors called activators
Untranslated regions of mRNA
Portions of mRNA at 5’ and 3’ ends **Not translated into protein *5’ UTR upstream from coding sequence •Recognized by ribosomes to initiate translation •3' UTR found following a stop codon
• Three key modifications to mRNA before leaving nucleus
1)• 5’ capping Addition of 7-methylguanosine to 5’ end Distinguishes mRNA from other RNA 2)• Splicing out of introns Occurs during transcription Introns always have two nucleotides at either end 3' splice site: AG 5’ splice site:GU • 3’ polyadenylation
Chain initiating and chain terminating codons
C i= AUG
C t= UAA UAG UGA
mRNA splicing(process)
RNA Splicing
•primary transcript combines with snRNPs (small nuclear ribonucleoproteins)
• snRNPs and mRNA forms “spliceosome”
• Loop of mRNA with intron is formed (“lariat”)
• Lariat released → removes intron
How many proteins are formed from 1 gene
Alternative Splicing • Allows many proteins from same gene • DNA: Exon1 – Exon 2 – Exon 3 – Exon 4 … Exon 10 • Protein 1: Exon1 – Exon 3 – Exon 7 • Protein 2: Exon 2 – Exon 5 - Exon 10
How transcription terminates
Enzyme
3’ Polyadenylation
• Occurs at termination of mRNA transcription
• Triggered by specific DNA/RNA sequences
• “Polyadenylation signal:” AAUAAA
• AAUAAA followed by 10-30 nucleotides then CA
Leads to termination of
transcription
3’ Polyadenylation
3’ Polyadenylation
• Enzyme: Poly-A polymerase (PAP)
Adds ~200 adenosine nucleotides to 3’3’ end mRNA
Nucleotides are formed in which way
New nucleotides are always arranged from 5’ prime to 3’ prime
3 main lipids of lipid bilayer
Composition of Outer and inner leaflet of c.m
Phospholipid+cholesterols+sphingolipids
Outer leaflet=phosphotidyl choline+sphingolmyelin
Inner leaflet= phosphotidyl (serine+ethanolamine)
What can pass through cm
Lipid soluble substances i-e 02,CO2, alcohol etc
How cell knows if ATP is depleted
When ATP breaks into cAMP and cAMP activates glycogen splitting enzyme phosphorylase that break glycogen into glucose
peroxisomes 2 differences from lysosomes 2 enzymes 2 functions
Either self replicatory or made from SER instead of golgi apparatus and have oxidases instead of hydrolases
Oxidase make H2O2 catalase that’s also an oxidase
Half of alcohol —> acetaldehyde
Catabolize large chain fatty acids
Whats the only mean of transportation of macromolecules such as proteins
Pinocytosis
Phagocytosis occurs when cells engulf large bodies such as whole cells, bacteria etc
Coated pits and clathrin
Group of receptors concentrated at a point are called coated pits
Catherin are fibrillar proteins that start pinching inward along with the help of actin and myosin
Glycocalyx and it’s function
Glycocalyx is negatively charged glycoprotein and glycoprotein that us present around cell membrane it is mainly composed of carbohydrates .it differentiate cm from other intercellular membranes and acts as barrier
Gap junction
Also called as nexus Allow the movement of ions and chemicals b/w cells present in heart and basal epithelial cells of intestinal mucosa
Each gap junction has two halves each half is surrounded by 6 protein subunits called connexins
Desmosomes
Hemidesmosomes
Desmosomes are also called as macula adherens they combine cell to cell by intermediate filaments they function like tight junctions
H… are cell to extracellular matrix junctions by intermediate filaments
What are the adherens junction and focal junction
Where they are present
They connect actin filaments of one cell to other by some transmembrane proteins called cadherins
Present in intercalated discs of heart and epidermis of skin
Connect actin filaments of cell to extracellular matrix by proteins called integrins present in epithelial lining
