Topic 4A - DNA, RNA and Protein synthesis Flashcards
Is DNA stored differently or the same in different organisms?
It is stores different in different organisms
How do eukaryotic cells store DNA?
They store DNA as linear chromosomes - thread-like stuctures each made up of one long molecule of DNA. These are usually found in nucleus
Describe the structure of a eukaryotic linear DNA molecule (chromosome)?
- They are really long, so its wound up to fit in nucleus
- They are wound around proteins called histones (which help support DNA)
- DNA (with protein) is coiled up very tightly to make compact chromosome (DNA double-helix)
What kind of DNA to mitochondria and chloroplasts have?
They have DNA similar to prokaryotic cells as its circular and shorter than DNA molecules in nucleus.
- This type of DNA is not supported by histone proteins
What is the difference between prokaryotic and eukaryotic DNA?
- Prokaryotic DNA is shorter and circular
2. Prokaryotic DNA isnt wound around histones - it condenses to fit in cell by supercoiling
What is a gene?
a sequence of DNA bases that codes for either a polypeptide or functional RNA (RNA molecules, other than mRNA, that perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA)
What determines the order of amino acids in a polypeptide?
The order of bases in a gene
How is each amino acid coded?
They are coded for by a sequence of 3 bases in a gene called a triplet
What is the 1st stage of making a polypeptide (1st stage of protein synthesis)?
DNA is first copied into messenger RNA
What is a genome?
The entire DNA of an organism
What is a proteome?
The full range of proteins that a cell is able to produce
What are introns?
They are the sections of a gene that dont code for amino acids
What are exons?
They are the sections of a gene that do code for amino acids
Do introns affect the order of amino acids?
No as they are removed during protein synthesis
What is the purpose of introns?
Unknown
What are non-coding repeats?
They are regions of multiple repeats outside of genes e.g. CCTTCCTTCCTT
- They dont code for amino acids either
What forms do genes exist in?
in the form of alleles
What does it mean if the order of bases in every allele is slightly different?
It means that they code for slightly different versions of the same polypeptide e.g. the gene that determines blood type exists as one of 3 alleles - O, A and B
How many pairs of chromosomes do humans have in total?
23
What are homologous pairs?
Pairs of matching chromosomes that are the same size, and have the same genes, but could have different alleles
How would you know if alleles codes for the same characteristic in a homologous pair?
(DIAGRAM)
They should be found at the same fixed position (locus) on each chromosome
What is the main difference between RNA and DNA?
- RNA is a single polynucleotide strand, whilst DNA is a double helix
- It contains uracil, instead of thymine
Describe the structure and function of mRNA
DIAGRAM
Structure:
- It is a single polynucleotide strand
- In mRNA, groups of 3 adjacent bases make up a codon/triplet code/base triplets
Function:
- Carries the genetic code from DNA to ribosomes, where its used to make a protein during translation
Describe the structure and function of tRNA
DIAGRAM
Structure
- a single polynucleotide strand folded into a clover shape (Hydrogen bonds between base pairs hold molecule in clover shape)
- Has a specific sequence of 3 bases at 1 end called anticodon
- Has an amino acid binding site at other end
Function:
- Carries amino acids, used to make proteins, to the ribosomes
Where does transcription take place in:
- Eukaryotic cells?
- Prokaryotic cells?
Eukaryotic cells - Nucleus
Prokaryotic cells - cytoplasm
Describe steps 1-3 of transcription
DIAGRAM
1- Hydrogen bonds between DNA strands breaks, separating strands, and DNA molecule uncoils at that point, exposing some of the bases
- One strand is used as template to make mRNA copy
- Specific, complementary base pairing allows mRNA strand to be complementary to DNA template strand
- RNA polymerase attaches to DNA double-helix at the beginning of gene and joins nucleotides together.
- Hydrogen bonds between uncoiled strands of DNA re-form after RNA polymerase has passed, forming double-helix again
- When enzyme reaches particular sequence of DNA called a stop signal, it stops making mRNA and detaches from DNA
- Splicing occurs and mRNA moves out of nucleus through nuclear pore and attaches to ribosome
What is pre-mRNA?
mRNA strands containing introns and exons.
- In eukaryotes, introns and exons are copied into mRNA during transcription
What is splicing?
A process that occurs in the nucleus in eukaryotes, where introns are removed and exons are joined together - forming mRNA strands
- mRNA then leaves nucleus to the ribosome
Does splicing take place in prokaryotes?
No as prokaryoes have no introns, so theres no need
Where does TRANSLATION occur in:
- Eukaryotes?
- Prokaryotes?
In both, it occurs at the ribosomes in the cytoplasm?
Describe steps 1-3 of TRANSLATION
DIAGRAM
- mRNA attaches to ribosome and tRNA molecules carry amino acids to it. ATP provides energy needed for bond between amino acid and tRNA to form
- tRNA (carrying amino acid), with anticodon complementary to 1st codon on mRNA, attaches to it mRNA by specific base pairing.
- 2nd trRNA attaches itself to next codon in same way
4- 2 amino acids attached to tRNA molecules are joined by peptide bond. tRNA moves away, leaving it alone
5- 3rd tRNA binds to next codon on mRNA. It’s amino acid binds to first two (amino acids) and 2nd tRNA moves away
6- Process continues to produce chain of linked amino acids (polypeptide chain) until theres a stop signal on mRNA molecule
7- Polypeptide moves away from ribosome
What is the main point of:
- transcription?
- translation?
Transcription: To produce mRNA copy of gene, from DNA
Translation: To join up amino acids to make polypeptide chain, following sequence of codons carried by mRNA
Whats another word for protein synthesis?
Polypeptide synthesis
What is the ‘genetic code’
The sequence of base triplets in mRNA which code for specific amino acids
What does it mean if the genetic code is ‘non-overlapping’?
Non-overlapping: in genetic code, each base triplet is read in sequence, separate from triplet before it and after it and base triplets dont share their bases
What does it mean if the genetic code is ‘degenerate’?
Degenerate: There are more possible combinations of triplets than there are amino acids (20 acids but 64 combos). This means that some amino acids are coded for by more than 1 base triplet e.g. Tyrosine can be coded for by UAU and UAC
What does it mean if the genetic code is ‘universal’?
Universal: The same specific base triplets code for the same amino acids in all living things
look at quesions on interpreting data ABOUT NUCLEIC ACIDS
look in book
look at questions on interpreting data about THE ROLE of nucleic acids
look in book
