DNA, genes and chromosomes Flashcards
What is a chromosome
A thread like structure that contains coiled up DNA, genes and proteins
What is DNA like in prokaryotes
- Singular circular chromosomal DNA molecule sometimes refers
as a nucleoid - Contain plasmids which are more accessible for proteins required for gene expression and therefore contain genes that are required often and quickly.
- Genes for antibiotic resistance are often found in plasmids
- Not associated with proteins and is smaller than eukaryotes
- The DNA condenses to fit in the cell by super coiling
What is DNA like in eukaryotes
- Chromosomes made of very long condensed DNA molecules
- associated with proteins
- main proteins are histones (roles is to organise and condense DNA tightly so it can fit in the nucleus)
- Other proteins are enzymes used in copying and repairing DNA
- Tightly coiled DNA and proteins are called chromatin
- In Interphase DNA replicates creating 2 sister chromatids
- Each chromatid is made up of one very long DNA molecule made up of a series of gene
What is a histone and what does it do in eukaryotic DNA
A histone is a large positively charged globular protein
Its role is to organise and condense DNA tightly so it can be fit into the nucleus
What is on the end of every chromatid in eukaryotic DNA
The ends are sealed with protective structures called telomeres
What is the DNA in mitochondria and chloroplast
what is the names given
Mitochondrial DNA (mt DNA)
found in the matrix
Chloroplast DNA (cp DNA)
found in the stroma
- Similar to DNA in prokaryotes
It is short, circular and not associated with proteins
What are genes and
what are the molecules
and what do genes do in DNA
A base sequence of DNA that codes for a sequence of amino acids in a polypeptide chain or a functional RNA molecule (required for protein synthesis)
mRNA - Messenger RNA used by ribosomes to form polypeptide chains
tRNA - Amino acids carried to ribosomes by transfer RNA
rRNA - Ribosomal RNA form part of structures of ribosomes
genes in DNA control protein structure as they determined the sequence amino acids join together when proteins are synthesised
What is the genetic loci
and how can genes exist
It is the position of a gene on a chromosome is its locus (loci)
Genes can exist in 2 or more different forms called alleles that have slightly different nucleotide sequences but occupy same locus of a chromosome
What are alleles
Two or more different versions of gene
What are triplet codes and what do they do
what can they be known as?
Triplet codes are
- DNA base codes found within a gene
- A sequence of 3 base codes code for one amino acids
But also some triplet codes can code for the start of stop signals of chains
These triplet of bases are known as codons e.g. CAG
What are the features of the triplet code
- The code is non overlapping
- The code is degenerate
- The code is universal
Why is the triplet code non-overlapping
This ensures the cell reads the DNA correctly and can produce the correct sequence of amino acids it requires to function properly
Each base is only read once
Why is the triplet code degenerate
There are 4 bases so there are 64 different triplets possible. But there’s only 20 amino acids . This result in many codons coding for the same amino acids
so is degenerate
This means a change in the genetic code doesn’t necessarily result in a change amino acids
e.g C,A,G meaning mRNA code G,U,C that also codes for the same amino acids
Why is the triplet code universal
- Almost every organism uses the same code meaning some codons code for the same amino acids in all living things (genetic info transferable through species)
What is non-coding DNA
where can it be found
what happens during transcription
Genome in eukaryotic cells contain non-coding sections of DNA
- Non coding DNA - doesn’t code for amino acids
- It can be found between genes - this means they contain the same base sequence’s repeated multiple times
- Can also be found withing genes as introns and coding exons can be separated by one or more introns
. During transcription, eukaryotic cells transcribe the whole gene (all introns and Exons) and produce pre-mRNA molecules
. Before the pre-mRNA molecules leave the nucleus non-coding sections (introns) are removed and coding sections (exons) join together
process is called splicing
What is an Intron and Exon
Intron - Non -coding DNA
Exon - Coding DNA
What is a homologous pair
two chromosomes that contain the same genes
