DNA and cell division Flashcards
What is a genome?
the entire DNA (genetic information) of an organism
What is a gene?
a section of DNA coding for a specific protein
What is a chromosome?
A single strand of DNA found in the cells’ nucleus
Where are genes found in the cell?
on the chromosomes
Where are chromosomes found in the cell?
in the nucleus
What are the three components of a nucleotide?
phosphate, (deoxyribose) sugar and nitrogenous (or organic) base
What are the four organic (nitrogenous) bases in DNA?
Adenine, Thymine, Cytosine and Guanine
What makes up the backbone of a DNA strand?
Sugar and phosphate groups - repeating
How do the organic (nitrogenous) bases pair in DNA?
Adenine with Thymine and Cytosine with Guanine
Describe the shape of a DNA strange
Coiled to form a double helix
Give three differences between the structure of DNA and RNA
RNA is single stranded and DNA is double stranded.
RNA contains Uracil instead of Thymine.
The sugars are different (RNA contains ribose, DNA contains deoxyribose)
Describe the steps in transcription
DNA helicase uncoils the DNA and separates the two strands.
RNA nucleotides are attracted to the complementary bases on the template strand of DNA (Uracil pairs with Adenine).
RNA polymerase forms bonds between the nucleotides.
mRNA molecule separates from DNA and leaves the nucleus.
DNA strands are attracted to each other again and recoil.
Describe the steps in translation
mRNA binds with ribosome, with two codons (triplets of bases) in place.
tRNAs with complementary anticodons are attracted to the mRNA.
tRNAs have attached the amino acid corresponding to the codon.
Ribosome catalyses the reaction to join the two amino acids together.
First tRNA leaves and the mRNA moves through the ribosome so the next codon is in place.
A tRNA with the correct anticodon is attracted and the amino acid is bound to the growing chain.
This continues until the end of the mRNA is reached.
What is the purpose of transcription?
Copying a gene as RNA, so that it can leave the nucleus and travel to the ribosome
What is the purpose of translation?
To make the protein coded for by a particular gene (RNA)
What is the function of mitosis?
To produce genetically identical daughter cells for growth, repair of tissue and asexual reproduction
What happens to the chromosomes in mitosis?
Chromosomes line up at the centre of the cell and the copies separate, moving to the edges of the cell before cell division occurs
Describe the key features of the cells produced in mitosis
Two daughter cells with a full (diploid) set of chromosomes, genetically identical to original cell
What is the function of meiosis?
To produce genetically varied gametes
What happens to the chromosomes in meiosis?
Division 1: pairs of chromosomes line up at the centre of the cell and separate, one chromosome moving to either end before cell division.
Division 2: individual chromosomes line up at the centre of the cell and the copies separate, moving to the edges of the cell before division occurs
Describe the key features of the cells produced in meiosis
Four daughter cells with one of each chromosome (haploid), half the genetic information of the original cell.
Each cell has a different combination of chromosomes
What causes genetic variation in offspring from the same parents?
Meiosis produces genetically different cells. Random fusion of gametes from mother and father
What are the differences between mitosis and meiosis?
Mitosis produces 2 daughter cells, meiosis 4.
Mitosis involves one cell division, meiosis 2.
Mitosis produced dipolid cells, meiosis produces haploid cells.
In mitosis, the daughter cells are genetically identical to both each other and the original cell, in meiosis they are genetically different.
Mitosis is for growth, repair and asexual reproduction, meiosis produces gametes for sexual reproduction.
What is meant by a diploid cell?
Contains pairs of chromosomes (so the cell has two copies of each gene)
What is meant by a haploid cell?
Contains one of each chromosome (only one copy of each gene)
What is the diploid number in humans?
46
What is the haploid number in humans?
23
What are the causes of variation (differences) between individuals of the same species?
genetic differences, the environment or a combination of both
What is a mutation?
a change in the sequence of bases in DNA
How does a mutation result in a changed characteristic?
it may result in a changed amino acid sequence in a protein, which can alter the shape (and therefore the function) of the protein
Describe the possible effects of a mutation on a phenotype (characteristic)
Many mutations have no effect.
Some have a small effect and very few have a large effect.
The effect may be beneficial (result in a new, useful trait) or may be harmful (a protein may no longer function)
Exposure to two things can increase the rate of mutation. What are they?
Ionising radiation (e.g. gamma rays or x-rays) or chemicals (mutagens).
What is the name used to describe chemicals which cause mutations leading to cancer?
Carcinogens
