Biology - Genes & Protein Synthesis - Chapter 8

What is a gene

A base sequence of DNA that codes for a polypeptide chain and a functional RNA molecule

What is a locus

Location of a gene on chromosome

What is an allele

Different forms of the same gene

What is a homologous pair

Pairs of chromosomes with same size and genes but might have different alleles

How is DNA stored in a eukaryote

• DNA is tightly wrapped around histones to fit as chromosomes in the nucleus

• chromosomes are linear

How is DNA stored in a prokaryotic cell

• DNA is shorter and circular

• DNA is not wrapped around histones

• DNA in mitochondria and chloroplasts are similar to prokaryotic DNA

Features of genetic code

• Degenerate → multiple codons code for the same amino acids (limits mutation)

• Non-overlapping → each base is read once and is part of one codon (if mutation occurs, it only affects 1 codon ∴ 1 amino acid)

• Universal → same codons code for same amino acids in all organisms (allows genetic engineering)

Genome & Proteome definition

• Genome → complete set of genes an organism has

• Proteome → full range of proteins in a cell

• Genome never changes, however proteome does

What are introns and exons

• Intron → dont code for amino acids & get spliced from mRNA

• Exons → sections of DNA that code for amino acids

what is RNA

• has ribose sugar, a nitrogenous base and a phosphate group

• copies and transfers genetic code from DNA to ribosomes

what is mRNA

• single stranded copy of DNA, created in nucleus and leaves to carry genetic code to ribosome because DNA is too big and can be damaged by enzymes

what is tRNA

• single stranded w/ clover leaf shape held together by hydrogen bonds

• transfers amino acids to ribosome

• specific amino acids attach to tRNA molecules which are determined by anticodons which are complementary to mRNA codons

what is rRNA

binds with proteins to make ribosomes

Differences between DNA and RNA

• DNA is double stranded while RNA is single stranded

• DNA has thymine while RNA has uracil

• DNA has deoxyribose sugar while RNA has ribose sugar

• DNA is longer while RNA is shorter

What are the stages of protein synthesis

• Transcription - DNA is transcribed & an mRNA molecule is produced

• Translation - mRNA joins a ribosome and an amino acid sequence is produced

Describe the process of transcription

• DNA helicase unzips strands by breaking hydrogen bonds

• One strand acts as a template strand

• Free mRNA nucleotides bind to DNA strand via complementary base pairing

• RNA polymerase joins strands by forming phosphodiester bonds in backbone

• Once copied, mRNA is modified (spliced) then leaves nucleus through nuclear envelope pores

Describe the process of translation

• mRNA binds to ribosome at start codon

• tRNA molecules with anticodons that are complementary to mRNAs codons bind to specific amino acids and bring them to mRNA on ribosome

• two tRNAs fit on ribosome at once

• peptide bond forms between amino acids using ATP

• ribosome moves along mRNA until stop codon is reached and it detaches

• the polypeptide chain is now created and moves to the golgi for folding and modification

Differences between mitosis and meiosis

• Mitosis produces two genetically identical daughter cells while meiosis produces four genetically different daughter cells

• Mitosis has diploid daughter cells while meiosis has haploid daughter cells

• Mitosis has 1 division while meiosis has 2

How does genetic variation occur

• independant segregation

• crossing over

process of meiosis

• interphase happens before meiosis where DNA is replicated

• in the first division, homologous chromosomes pair up then separate and two haploid cells are produced

• in the second division, sister chromatids are separated then four haploid cells are produced

what is independent segregation

• occurs in metaphase

• homologous chromosomes line up at equator

• maternal and paternal chromosomes are randomly pulled to each pole

• the pairs are separated so 1 of each homologous pair ends up in the daughter cells

what is crossing over

• regions of non sister chromatids are exchanged within homologous pairs

• chromatids become twisted which causes tension so they break and when they recombine, new combinations of alleles are made

What is a gene mutation

change of sequence of base pairs in DNA that may result in an altered polypeptide

what is an insertion mutation

• involves the addition of an amino acid and changes the amino acid that has been coded for

• changes all future amino acids so it significantly changes the polypeptide, resulting in a non-functioning protein

what is a deletion mutation

• changes sequence of amino acids

• might not be significant because it could occur at end codon

types of substitution mutations

• silent mutation → no change in amino acids

• missense mutation → change in 1 amino acid

• nonsense mutation → premature stop codon

what is genetic diversity

the number of different alleles of genes in a population

what is natural selection

• leads to evolution, which is the change in allele frequency over many generations in a polulation

• results in species becoming better adapted for their environment

what types of adaptations are there

• anatomical → body

• physiological → body’s systems e.g. ur heart beats fast when ur scared

• behavioural

describe the process of natural selection

• new alleles for gene are created by random gene mutation

• new alleles increase survival chance in that environment so they are more likely to survive and reproduce

• new genes are passed onto next generation

• over time, frequency of allele increases in the population

types of natural selection

• directional → occurs when there is a change in the environment & extreme traits have selective advantage

• stabilising → occurs when there is no change in the environment & modal trait has selective advantage