8: DNA, genes and protein synthesis Flashcards
What is a gene?
A sequence of DNA bases that codes for the amino acid sequence of a polypeptide OR a functional RNA
What are the different RNA forms?
rRNA - Ribosomal
tRNA - Transfer
mRNA - Messenger
How does DNA exist in eukaryotic cells?
Linear DNA molecules that exists as chromosomes
One long molecule of DNA
Found in the nucleus coiled very tightly
How is a DNA wound in eukaryotic cells?
Really long so wound up around histone proteins to fit in nucleus
What is a histone?
A protein that DNA is wound around in eukaryotic cells
Supports the DNA
Other than the nucleus, where is DNA found in a eukaryotic cell?
Mitochondria and chloroplasts
Circular and shorter - no histones
How does DNA exist in prokaryotic cells?
Shorter than chromosomes and circular
No histones
Super-coiling so it fits in the cell
What is a cell’s genome?
Complete set of genes in the cell
What is a cells’ proteome?
Full range of proteins that a cell is able to produce
What does the order of bases determine?
The order of amino acids to form a particular polypeptide
What is an amino acid coded by ?
DNA Triplet
Three bases from a gene
What is the use of genes that don’t code for polypeptides?
Codes for functional RNA
What is functional RNA?
RNA other than mRNA
Performs special tasks (tRNA & rRNA)
What is a chromosome?
A thread-like structure made of protein and DNA
What is an allele?
One of a number of alternative forms of a gene
What is the locus?
Position of a gene on a chromosome/DNA molecule
What is a gene?
A section of DNA on a chromosome coding for the amino acid sequence for one or many polypeptides
What does homologous mean?
A pair of chromosomes, one maternal and one paternal
Same gene loci therefore determines same features
What is degenerate code?
This is when amino acids are coded for by more than one triplet of bases
What is an intron?
Non-coding sequences of DNA in a gene
What is an exon?
Sequences of bases that code for amino acids in a gene
Do prokaryotic cells contain introns?
No
Why is the rate of replication faster in prokaryotic cells?
No membrane has to be synthesised
How many different bases are there in DNA?
4 different bases
How many different triplets are there and how is this number found?
64
4 bases ^3 = 64
How is genetic code universal?
Same specific base triplets code for same amino acids in all living things
What are triplets than do not code for an amino acid?
Nonsense triplets
What are stop triplets?
Stop signals to terminate a protein chain
Why does DNA need to be transcribed to RNA?
DNA confined to nucleus as too large to move through nuclear pores
Protein synthesis occurs in cytoplasm
What is a codon?
Sequence of three bases of mRNA that codes for an amino acid
Why are introns removed for protein synthesis?
To prevent gaps in the amino acid sequence which would cause gaps in the protein
What is the difference between DNA & RNA?
RNA is a single strand Contains uracil (U) instead of thymine (T)
What are the characteristics of messenger RNA (mRNA)?
Single strand & single helix Located in nucleus & cytoplasm Bases: AUGC Ribose sugar Function: Transcription
What are the characteristics of DNA?
Double strand & double helix Located in nucleus Bases: ATGC Deoxyribose sugar Function: Hereditary material
What are the characteristics of transfer RNA (tRNA)?
Single strand & clover-leaf Located in cytoplasm Bases: AUGC Ribose sugar Function: Translation
What is the function of transfer RNA?
Carries amino acids for proteins to ribosomes
Each tRNA has a specific sequence of three bases at one end, called an anticodon
They have an amino acid binding site
What are the two main stages of protein synthesis?
Transcription
Translation
What occurs in transcription?
DNA is used to synthesise a molecule of mRNA that will carry the code to the ribosomes
Describe the transcription process
DNA helicase breaks hydrogen bonds and exposes nucleotides
RNA polymerase binds to promoter region and adds free nucleotides to form pre-mRNA
Stops once it reaches a stop region
pre-mRNA leaves the nucleus by the nuclear pores
What is pre-mRNA?
Newly formed mRNA which contains exons and introns
Also contains promoter regions
What is a promoter region?
Recognition sites for the RNA polymerase that indicate where to start copying the DNA
What is splicing of pre-mRNA?
The removal of the introns and remaining exons are joined together
Ends of mRNA is “capped” which allows recognition which is required for translation
How are amino acids joined to tRNA?
Using energy from ATP and a specific enzyme
What organelle is required for translation?
Ribosomes
What base sequence is always found on tRNA and why?
ACC
This is where amino acids bind
Where does translation occur?
In the cytoplasm at the ribosomes
What occurs in translation?
Amino acids are joined to create a polypeptide chain
This is done using the codons from mRNA to determine specific amino acids
Describe the translation process
mRNA attaches to ribosome and tRNA carries amino acids to it
tRNA molecule with anticodon attaches to complementary bases on codon on the mRNA
This occurs with another tRNA and the amino acid from each are joined by a peptide bond
This continues until it reaches a stop codon
What happens to the tRNA after the amino acid has formed a peptide bond with another in the ribosome?
It moves away from the ribosome
Leaves the amino acids behind
How can the genetic code be described?
Non-overlapping
Degenerate
Universal
Why is the genetic code described as non-overlapping?
As the base triplets don’t share their bases
What is the role of RNA polymerase in transcription?
Join and attach nucleotides to form an RNA molecule
Why can splicing cause a gene to code for different proteins?
The exons can be joined in different orders to produce different proteins
Mutation of protein question answer
Change in DNA, base sequence, triplet
Different amino acids used to make a protein
Different sequence and primary to tertiary structure
Different tertiary means different bonds form
Protein has different shape
(enzymes active site changes so no enzyme-substrate complex can form)
