4A - DNA, genes and chromosomes Flashcards
What is nuclear eukaryotic DNA like?
Linear and associated with proteins.
Eukaryotic cells contain linear DNA molecules that exist as what?
Chromosomes.
What are chromosomes?
Thread-like structures, each made up of one long molecule of DNA.
Where are chromosomes found?
In the nucleus.
How can the DNA molecule fit into the nucleus?
It has to be wound up as it is really long.
What is the DNA molecule wrapped around to fit into the nucleus?
Proteins called histones.
Apart from providing a base for DNA to wrap around, what is the function of histone proteins?
Help support the DNA.
After the DNA has been wound up to fit into the nucleus, what happens to the DNA?
The DNA (and protein) is then coiled up very tightly to make a compact chromosome.
What organelles in eukaryotic cells also have their own DNA?
The mitochondria and chloroplasts.
What is the DNA like in mitochondria and chloroplasts?
Pretty similar to prokaryotic DNA because it is circular and shorter than DNA molecules in the nucleus.
It is not associated with histone proteins.
What is prokaryotic DNA like?
DNA molecules are shorter and circular.
How do prokaryotes carry DNA?
As chromosomes.
How does prokaryotic DNA fit into the cell?
It condenses to fit in the cell by supercoiling.
What is a gene?
A sequence of DNA bases that codes for either a polypeptide or functional RNA.
What does the sequence of amino acids in a polypeptide form?
The primary structure of a protein.
What do different polypeptides have in terms of amino acids?
A different number and order of amino acids.
What determines the order of amino acids in a particular polypeptide?
The order of bases in a gene.
What does the order of bases in a gene determine?
The order of amino acids in a particular polypeptide.
What is each amino acid coded for by?
A sequence of three bases in a gene called a triplet.
What is a triplet?
A sequence of three bases in a gene.
What does a triplet do?
Codes for an amino acid.
What is the first stage in making a polypeptide/the first stage of protein synthesis?
DNA is first copied into messenger RNA (mRNA).
What is an amino acid made up of?
A sequence of 3 bases in a gene.
What do genes that don’t code for a polypeptide do instead?
Code for functional RNA.
What is functional RNA?
RNA molecules other than mRNA, which perform special tasks during protein synthesis, e.g. tRNA and ribosomal RNA (rRNA), which forms part of ribosomes.
What is a genome?
The complete set of genes in a cell.
What is a proteome?
The full range of proteins that the cell is able to produce.
Genes that do code for polypeptides contain what?
Sections that don’t code for amino acids called introns.
What are introns?
Sections of a DNA/gene that don’t code for amino acids.
What are all the bits of a gene that code for amino acids called?
Exons.
What are exons?
All the bits of a gene that code for amino acids.
When are introns removed from DNA?
During protein synthesis.
Why are introns removed during protein synthesis?
So they don’t affect the amino acid order.
Does prokaryotic DNA have introns?
No.
Does eukaryotic DNA have introns?
Yes.
What is the purpose of introns?
The purpose isn’t known for sure.
What does eukaryotic DNA contain outside of genes?
Regions of multiple repeats.
Where are regions of multiple repeats found?
Outside of the genes in eukaryotic DNA.
What are multiple repeats?
DNA sequences that repeat over and over.
E.g. CCTTCCTTCCTT.
What are the regions of multiple repeats outside of genes called?
Non-coding repeats.
What are non-coding repeats?
Repeat areas that don’t code for amino acids for example multiple repeats outside of genes.
Genes can exist in different forms called what?
Alleles.
What is an allele?
A different form of a gene.
What is the order of bases in each allele like?
Slightly different.
What does the order of the bases in different alleles being different mean they do?
They code for slightly different versions of the same polypeptide.
How many alleles of the gene that determines blood type are there?
3 - one determines O, one A and one B.
How many pairs of chromosomes do humans have?
23.
What are pairs of matching chromosomes called?
Homologous pairs.
What is a homologous pair?
A pair of matching chromosomes.
Describe the chromosomes in a homologous pair:
Both chromosomes are the same size and have the same genes, although they could have different alleles.
Alleles coding for the same characteristic will be found where on each chromosome in a homologous pair?
At the same fixed position (locus) on each chromosome in a homologous pair.
What is diploid number?
The number of chromosomes - 46 in humans.
What are antiparallel strands in DNA?
The strands run in opposite directions so their 3’ and 5’ ends are at opposite ends.
Describe what a gene is
A gene is a unit of heredity. A section of DNA on homologous chromosomes at a specific position (the locus). Carries the information to produce the amino acid sequence of a polypeptide.
Describe what is meant by the term ‘homologous chromosomes’?
In eukaryotes each normal body cell contains 2 copies of each type of chromosome (homologous pairs).
What is meant by the diploid number?
Humans have 46 chromosomes (diploid number) i.e. 23 homologous pairs.
What is an allele?
A version of a gene.
Define the term mutation?
Any changes in the base sequence of a gene produces a new allele for that gene. This will lead to the production of a different polypeptide, and therefore a different protein. This protein may not function properly or at all (eg. enzyme).
