Topic 4- DNA and Protein synthesis Flashcards
What is protein synthesis?
The productions of proteins (polypeptides) from the information conatined within a cells DNA
What are the 3 main stages of protein synthesis?
-Transcription
-Processsing of the mRNA (splicing)
-Translation
What is transcription?
-Where the DNA code is copied into mRNA
What is translation?
-Where the mRNA joins with a ribosome and the code it carries is used to synthesise a protein
What is RNA, mRNA and tRNA
-A single polynucleotide strand
What base does RNA contain instead of thymine?
-Uracil
When is mRNA made?
-During transcription
What is the function of mRNA?
-It carries the genetic code from the DNA to the ribosomes where it is used to make a protein during translation
In mRNA what are the groups of 3 adjacent bases called?
-Codons
What is the function of tRNA?
-Involved with the process of translation
-It carries the amino acids that are used to make proteins to the ribsomes
What is the structure of tRNA?
-Single polynucleotide strand thats folded into a clover shape
-Hydrogen bonds between specific base pairs hold the molecule in this shape
in tRNA what are the specific sequence of 3 bases at one end called?
-Anticodon
What does tRNA have at its other end?
-An amino acid binding site
Where is mRNA found in the cell?
-Nucleus
Where is tRNA found in a cell?
-In the cytoplasm
Does mRNA have hydrogen bonds?
-No
Is mRNA or tRNA longer?
-mRNA
What is a genome?
-The complete set of genes in a cell,including those in the mitochondria and chlorplast
What is a proteome?
-The full range of proteins produced by a particular genome
Step 1 transcription: When does transcription start?
-When RNA polymerase attaches to the DNA double helix at the begining of a gene
Step 1 transcription: How are the DNA strands separated?
-DNA helicase attached to RNA polymerase which break the hydrogen bonds between the strands
-The stranbds are separted and the DNA moleccule uncoils which exposes some of the base pairings
Step 1 transcription:How is an mRNA copy made?
-One of the strands is used a template strand
Step 2 transcription:How is complementary mRNA made?
-The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand
-The free bases are attracted ti the exposed bases
-Specific complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand
-Once the rNA nucleotides have paired up with their specific bases on the DNA strand they are joined together by RNA polymerase forming an mRNA strand
Step 3 transcription: How does the RNA polymerase move down the DNA strand?
-The RNA polymerase moves along the DNA assembling the mRNA strand
-The hydrogen bonds between the uncoiled strands of DNA reform once RNA polymerase has passed by and the strands coil back up into a double helix
Step 4 transcription:What is a stop signal?
-When RNA Polymerase reaches a sequence of DNA called a stop signal, It stops making mRNA and detaches from the DNA.
Step 4 transcription:Where does the mRNA move out of the nucleus from?
-Nuclear pores
-Attaches to a ribosome in the cytoplasm
Explain what happens during splicing?
-Introns are removed and the exons are joined together forming mRNA strands
-Takes place in the nucleus
-The mRNA then leaves the nucleus for translation
Why does splicing not take place in prokaryotic cells?
-mRNA is produced directly from the DNA
-No introns in prokaryotic DNA
Where does translation take place in eukaryotic and prokaryotic cells?
-The ribosomes, in the cytoplasm
What happens during translation?
-Amino acids are joined together to make a polypeptide chain, following the sequence of codons carried by the mRNA
What are the differences and similarities between DNA and RNA?
Differences:
Sugars:
-RNA+ribose
-DNA+deoxyribose
-Same chemical structure expect that ribsoe has a hydroxyl group on its 2nd carbon
-RNA is single stranded
-Rna is much shorter
-RNA has uracil instead of thymine
Similarities:
-Both nucleic acids
What does mRNA stand for?
-Messenger RNA
What does tRNA stand for?
-Transfer RNA
What are the differences between mRNA and DNA?
mRNA is:
-Single stranded
-Small enough to leave the nucleus via nuclear pores
-Ribose sugar
-Uracil instead of thymine
-Codons
What are introns?
-Regions of DNA which do not code or proteins
What are exons?
-Regions of DNA that code for proteins
Why do the introns need to be spiced out?
-To produce functional proteins
What molecule removes the introns?
-Spliceosome
What is pre-mRNA?
RNA that contains introns and exons
What is mature RNA?
RNA that only contains exons
Which strand moves in the 5’-3’ direction?
-Template strand
Which strand moves in the 3’-5’ direction?
-Coding strand/non template strand
Why is there a different number of nucleotides after transcription?
Introns are present in the DNA
How would copying bases more than once cause differentiation in the protein?
-Frameshift
-Changes in the base sequence of later triplets/ amino acid codes
Which DNA sequence would be more slippery CCC-GGG-GGG or CCG-GGG-GGG?
CCG-GGG-GGG- G is present more times
Describe translation
-Condensation reaction takes place and phosphodiester bonds form between the nucleotides
-mRNA strand leaves through the nuclear pores (in the nuclear envelope) and goes to the ribosome
-tRNA molecules bring specific amino acids to the ribosomes
-specific tRNA molecules for specific amino acids
-anticodon of tRNA is complementary to codon on mRNA
-peptide bonds form between the amino acids
-tRNA detaches and collects another amino acid
-ribosome moves along mRNA
What are the 3 roles of ATP in protein synthesis
-Provides energy required by the ribosome to move along the mRNA strand
-tRNA molecules use it to deliver specific amino acids
-ribosome detaches from the mRNA
