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A Level Biology > DNA, Genes And Protein Synthesis > Flashcards

DNA, Genes And Protein Synthesis Flashcards

(46 cards)

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1
Q

What are 4 features of the genetic code?

A

Degenerate
Non-overlapping
Universal
Read in triplets (codons)

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2
Q

What is meant by the term degenerate?

A

More than one triplet codes for the same amino acid

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3
Q

What is meant by non-overlapping?

A

Each base is read once (as part of a triplet)

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4
Q

What is meant by universal?

A

The same triplet always codes for the same amino acid in living organisms

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5
Q

Describe the structure of DNA?

A

Made of DNA nucleotides containing deoxyribose, phosphate and nitrogenous base (A,C,T,G)
It is double stranded and hydrogen bonds between complementary base pairs form a helix shape

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6
Q

How is DNA in eukaryotic cells different to prokaryotic cells?

A

DNA in eukaryotes is long and linear, associated with histone proteins to form chromosomes

DNA in prokaryotes is shorter, circular and not associated with histone proteins

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7
Q

What is the genetic code?

A

The order of bases on DNA, consists of codons (triplets of bases that code for a particular amino acid

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8
Q

Define the term gene?

A

A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids (polypeptide)

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9
Q

Define the term genome?

A

The complete set of genes in each cell of an organism

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10
Q

Define the term proteome?

A

The full range of proteins produced by the genome in that organism

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11
Q

What is a locus?

A

The fixed position on a chromosome occupied by a gene

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12
Q

What is an allele?

A

Different versions of the same gene, found at the same locus on a chromosome

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13
Q

What are exons and introns?

A

Exons = regions of DNA that code for amino acid sequences

Introns = non-coding regions of DNA

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14
Q

Where are introns located?

A

Introns are only present in eukaryotes not prokaryotes
They are found between exons in genes

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15
Q

What are the two different types of mutation?

A

Gene mutations
Chromosomes mutation

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16
Q

What are the two types of gene mutation?

A

Point mutation
Frame shift

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17
Q

What is a mutation?

A

A random change/alteration to the DNA base sequence which occurs randomly during DNA replication

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18
Q

What is a point mutation and give an example?

A

The mutation just effects one nucleotide/base
A base substitution ( a nucleotide in the DNA is replaced by another)

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19
Q

What are the three different ways a point mutation can affect the genetic code?

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A

A new triplet codes for a different amino acid due to the change in its tertiary structure
Triplet codes for same amino acid due to degenerate code
Triplet codes for a stop codon

20
Q

Why might a mutation not lead to a change in the amino acid sequence?

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A

Genetic code is degenerate so mutation may end up coding for the same amino acid as the original triplet
Mutation occurs in an intron

21
Q

What is a frame shift and give an example?

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A

All the subsequent amino acids changed as bases shift
(Base deletion/insertion)

22
Q

What is a mutagenic agent and give an example of this?

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A

Factors that increase the rate of gene mutation
- Ionising radiation eg.UV or X-Ray, Gamma ray
- Asbestos
- Carcinogenic chemicals eg.tobaco

23
Q

What is a chromosome mutation?

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A

Change in the number or structure of a chromosome

24
Q

What is a polyploid chromosome mutation?

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A

When an individual has 3 or more sets of chromosomes rather than 2

25
What is a chromosome non-disjunction ?
When chromosomes fail to separate correctly in meiosis so individuals (gametes) have one extra or one few chromosome
26
When does chromosome non-disjunction occur?
During meiosis in anaphase as the sister chromatids don’t separate
27
Describe the structure of mRNA?
A long, single strand, ribose sugars and AUCG bases It’s base sequence is complementary to the DNA it was transcribed from
28
What are the advantages of using mRNA instead of DNA for translation?
- mRNA is shorter and contains uracil = it breaks down quickly so no excess polypeptides are formed - mRNA is singe stranded and linear so ribosomes move along strand and tRNA binds to exposed bases - mRNA contains no introns
29
Describe the structure of tRNA
Single strand of nucleotides that are folded into a clover leaf shape due to hydrogen bonds One end is an anticodon and the other end is an amino acid binding site
30
What is produced by transcription?
mRNA
31
What are the two stages of protein synthesis?
1. Transcription 2. Translation
32
Where does transcription take place?
In the nucleus
33
Describe the process of transcription?
DNA helicase unwinds and separates the double helix by breaking hydrogen bonds between complementary base pairs It exposes bases on template strand, only one DNA strand acts as a template Free rRNA nucleotides align to complementary base pair on template In RNA uracil with pair with adenine RNA polymerase binds to template strand at the start triplet joining adjacent RNA nucleotides by phosphodiester bonds until it reaches the stop triplet Pre-mRNA is spliced removing introns to form RNA
34
What is produced by translation?
Polypeptides
35
Where does translation take place.
In the cytoplasm on ribosomes
36
Describe the process of translation?
mRNA associates with a ribosomes which binds to the start codon A specific tRNA molecule which has a complementary anticodon hydrogen bonds which o the start code bringing a specific amino acid As the ribosome moves along to the next codon another complementary specific tRNA anticodon binds until the stop codon Two amino acids are joined by peptide bonds in a condensation reaction using ATP
37
What is meiosis?
A form of cell division that produces 4 genetically different haploid cells (gametes)
38
What is the purpose of meiosis?
Meiosis ensures that when the gametes fuse at fertilisation, the normal diploid number of chromosomes is restored. Meiosisis also an important source of genetic variation
39
What is a diploid cell?
2n = there are pairs of each chromosome ( which are the same size and shape)
40
What s a haploid cell?
n = cells have a single copy of each chromosome
41
What is a homologous chromosome?
A pair of chromosomes (one maternal the other paternal) that have the same gene loci
42
What happens during meiosis I ?
The homologous chromosome are separated - Crossing over where homologous chromosome forms a bivalent before equivalent portions of genes(different alleles) are exchanges at the chiasmata - Independent segregation as homologous pairs randomly line up along the equator during metaphase I
43
What happens during metaphase II?
The sister chromatids are separated 4 genetically different haploid cells produced
44
Describe the differences between meiosis and mitosis?
Mitosis = 1 division, diploid daughter cells, genetically identical, chromosomes dealt with independently, chromatids separated, growth and repair Meiosis = 2 divisions, haploid daughter cells, division of homologous pair and sister chromatids, form gametes for sexual reproduction
45
DNA replication determines whether the chromosome has 1 or 2 chromatids Haploid or Diploid is whether each chromosome has a matching pair in the nucleus or not
DNA replication determines whether the chromosome has 1 or 2 chromatids Haploid or Diploid is whether each chromosome has a matching pair in the nucleus or not
46
How does meiosis cause genetic variation by producing new allele combinations?
Crossing over (prophase 1) Independent segregation (metaphase 1) Random fertilisation of gametes Random mating of organisms Mutations during DNA replication

A Level Biology (19 decks)

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