Lesson 13 - Cell Functions (58-93) Flashcards
Protein Synthesis
Proteins do everything and in every body system
This includes:
Transport/Carries
Channels / Pores
Antibodies
Storage and Structure
Hormones and Receptors
Contractile proteins
Enzymes
Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions (brings two things together so more likely to occur)
Polypeptides
Lots of short units of amino acids
Made up of amino acids
- Folds and bends (secondary structure)
A protein consists of one or more polypeptides (quaternary)
Primary Structure (Amino acid)
Secondary (alpha helix, 1)
Tertiary (Polypeptide chain)
Quaternary (multiple polypeptides)
Transcription and Translation
Transcription: DNA to RNA
Translation: RNA to Protein with help of ribosome
DNA direct protein synthesis
-one gene codes for 1 polypeptide
Ribosome are a cellular machinery for translation
DNA to RNA to Protein
Transcription:
Synthesis of mRNA (messenger RNA, single strand) under direction of DNA
-In nucleus
Translation:
Synthesis of polypeptide under
direction of RNA
-On ribosome in cytosol
RNA transcription
Catalyzed by RNA polymerase
-pries the DNA strand apart
-hooks together the RNA nucleotides
Follows base pairing rules
-uracil subs for thymine
Synthesis of a RNA transcription
3 stages: initation, elongation, termination
Initiation: Promotes signal initiation of RNA synthesis. Helps RNA polymerase to recognize promoter sequences. Indicates that transcription factors needed on RNA
Elongation: RNA polymerase moves along the DNA reading base pair. This untwists the double helix. Exposes 10-20 DNA bases at a time. DNA temp pairs with RNA nucleotides. Closes itself
Termination: Polymerase transcribes polyadenylation sequence (AAUAA) in pre-mRNA and beyond
-Protiens cut mRNA free (10-35 nucleotides after poly A)
-Polymerase falls away from DNA
RNA Processing after Transcription
Pre-mRNA
5’ end receives a modified G cap (protect). The 3’ end gets a poly-A tail
- Helps to export mRNA to cytosol
- Protects mRNA from degradation
- Helps ribosomes attach in cytosol
RNA splicing. Removes introns and joins exons
Introns=non coding
Exons =expressed (has genes)
RNA splicing - splicosomes
snRNP - small nuclear ribonucleoprotiens
-recognize splice sites, for introns and exons
Proteins
-modular structure
-each exon codes for different domain
Translation
Formation of protein using mRNA template
RNA is read is groups of three
codes for amino acid
codon=three nucleotides
mRNA carries message as a series of codons
Codons
Gene determines sequence of bases along mRNA molecule. Sequence of base triplets or codons. Codon either translated into an amino acid or serves as stop signal
Genetic universal code
64 options-codes for 20 amino acids including stop protein
Transfer RNA (tRNA)
Translation uses transfer RNA (tRNA’s) to shuttle amino acids to building polypeptide. Each tRNA is specific
for an amino acid (binds anticodon to complementary)
Anti-codon – binds to mRNA codon
RNA strand (~80 nucleotides)
~ L-shaped
Aminoacyl-tRNA synthetase
Joins each amino acid to the correct tRNA
Binding site specific to amino acid
Ribosomes
- Facilitate coupling of tRNA anticodons with mRNA codons during protein synthesis
-made of proteins and
ribosomal RNA or rRNA
has three binding sites for tRNA
The A site: “add”
The P site: “peptide”
The E site: “exit”
Translation into three stages
Initiation
Elongation
Termination
Initiation; Brings mRNA, initiator tRNA (with firsT Amino acid- Met) and two subunits of a ribosome together
-Start codon
Elongation: Amino acids are added one by one to polypeptide till reaches stop codon
Termination: ribosome reaches a stop codon in the mRNA
This is with a release factor getting a free polypeptide
